Helps with most of the problems:
(Don't forget to save screenshots if you have any)
Start -> Control Panel -> Add or Remove Programs
Search for Nostale and click on Remove
Delete Nostale Folder:
Start -> My Computer -> C -> Program Files (you can find the folder in here if you don't have GameforgeLive) -> GameforgeLive -> Games -> GBR_eng
Start -> Control Panel -> "Programs and Features"
Start -> PC settings -> System -> Apps & Features -> Search for Nostale -> Click on it and then uninstall
If there is still a folder for Nostale, just delete it. (Characters are saved online, they won't be deleted)
Now download Nostale again and install it (www.nostale.co.uk)
When you start Nostale you will see the patch window. On the left side below you can find a button for options. If you click on it you can change the graphic options. (E.g. DirectX -> OpenGL)
Legend: P = Problem, R = Reason, S = Solution
P: If you click on the link to download Nostale, the following text appears: The page could not be found (404 Error)
R: Server problems
S: Search in the forum if anyone already reported it. If nobody did, report it and wait.
P1: The download stops or doesn't finish but says it finished.
P2: Message: "The Setup files are corrupted. Please obtain a new copy of the program."
P3: Message "Unable to copy the file: Data is broken (CRC - Check)"
P4: Message "The Datas are broken"
R: In most cases the cause is your web browser.
S: Use a download manager. (en.wikipedia.org/wiki/Download_manager)
For the download manager you can use the following link:
P: When you double-click the installer your computer gets stuck.
R: The installer is large and your antivirus might be taking its time to check the files. If you have vista there's also a known issue when opening large files.
S1: Just wait 15 minutes.
S2: Windows XP:
Right-click the exe-data and click on "Run as". Now you can see the current user.
Remove the tick "Protect my computer and data from unauthorized program activity."
Click "Ok" and install Nostale.
S3: Restart your computer, deactivate your antivirus (temporarily) and double-click the installer.
P: NostaleX.dat/Nostale.dat found an error and has to be closed
R: Your graphic driver or Nostale might not be installed correctly or your Firewall blocks it "partly".
S1: Reinstall Nostale (see above)
S2: If reinstalling didn't work re-/install graphic driver.
S3: Configure your firewall correctly.
P: Nostale.exe found an error and has to be closed
S: Reinstall Nostale (see above) or change graphic options (see above)
P: Black screen after starting Nostale
S1: Change graphic options to OpenGL
S2: Activate window mode
S3: Install a new graphics card driver
P: NostaleX.dat wasn't able to find d3d9.dll
R: You don't have the latest version of DirectX.
S: Download DirectX
P: You click on start in the patch window and it disappears but nothing happens
R1: You're using Vista and after a certain patch you need to be administrator
R2: There are datas missing in your Nostale folder.
S1: Right-click on Nostale -> Properties -> Compatibility -> Tick "Run this program as an administrator" -> Apply
S2: Please check if the NostaleX.dat and the Nostale.dat are still in your Nostale folder. If you can't find them, reinstall.
If they're disappearing constantly, your antivirus might be deleting the files. Configure your antivirus correctly.
Always have at least 2,5 GB available on your computer.
P: You can't see the picture in the patch window.
R: Your firewall isn't configured correctly.
S1: Your Internet Explorer must be able to connect to the internet. (Check your settings)
S2: Configure your firewall correctly.
P: Server does not have http://download.gameforge.com/nostale_20150722/patch/de/Update.txt file.
R: The patch server probably crashed.
S1: Configure your firewall correctly. Your Internet Explorer must be able to connect to the internet.
S2: Search in the forum if it's already reported. If not, create a new thread, wait and try again later.
P: Can not connect to patch server
R: Your computer can't connect to the patch server.
S1: Configure your firewall correctly.
S2: Start Nostale as administrator.
S3: Wait and try again later.
P: Message: "Can't check the information. Please try again later"
R: The server is probably busy or your Firewall isn't configured correctly.
S1: Wait 10 minutes and restart your computer.
S2: Deactivate your firewall to test if it's working then or configure it correctly.
S3: Your Internet Explorer must be able to connect to the internet.
If none of this works you should contact your internet provider.
P: Message: "Error while making/changing the patch"
In case an error comes while receiving the patch files, system will collect error files for quick fix. The files will be in Nostale folder>>bugfile folder, and it may take some time due to the patch size. Send the copied file to 1:1 Q&A
R: Probably problems while connecting.
S1: Try again later. (Maybe the server is busy)
S2: Delete in your Nostale register the folder with the bugfiles -> the bugfiles and the temporary internetfiles of your Internet Explorer (Nostale is using IE) and try again.
S4: If you're using WLAN, try with LAN.
P: You want to log in but your Login information disappears after entering.
R: A problem with DirectX or your internet connection.
S1: Too many false attempts while entering your Login information, that leaded to a temporary ban. Try again later or restart your router. On the website is a function for forgotten passwords.
S3: Deactivate your antivirus/InternetSecurity/Firewall temporarily.
S4: If you're using an old version of Norton, try "norton removal tool" (could apply for later versions, too)
S5: Deactivate tools like Game Booster (If you're using one).
S6: Restart your router.
P: "The client is not the current version. Please download and install the updated client from the website."
R: You don't have the current version.
P: Your account has been banned. Please contact the NosTale Team.
R: You probably didn't stick to the rules: Game rules
S: Don't discuss your ban in the forum. If you want to complain about it, then write a ticket. You can write a ticket here: support.en.nostale.gameforge.com/
P: Your ID or password is incorrect.
S1: Open an editor an type in your data to see if you didn't activate capitalization or other settings.
S2: Go to the website and use the function for forgotten passwords. (www.nostale.co.uk)
S3: If you just registered you will have to activate your account using the link you will receive in an email.
S4: Programs like Sandbox can cause these problems. Try by uninstalling them.
P: This ID is currently in use.
R: You just got a disconnect or another person is using your account.
S1: Wait 2 to 5 minutes and try again. S2: If you relayed your Login information to someone, contact a GM. Or try to request a new password.
P: The server is currently undergoing maintenance. You can find the scheduled maintenance times on the NosTale website.
R: The maintenance is every Wednesday and will always be announced in the forum.
S1: Wait until it's over.
S2: Go to your Nostale folder and start Nostale.exe. If it's working then create a new shortcut for your desktop.
S3: Close Nostale, delete the "temporary internetfiles"/cache of IE and start Nostale again.
S4: Restart your computer and search for files with the ending .Pch (e. g. NostaleX.Pch.dat). If you find it delete NostaleX.dat and rename NostaleX.Pch.dat into NostaleX.dat
S5: If see that the Game is working for other players, reinstall Nostale correctly.
P: White pixels on your screen.
R: Nostale didn't patch correctly or incorrect graphic options.
S2: Change the Graphic settings and check if you have the latest version.
P: Characters or monsters look weird ( e. g. chickens look like Mimi Mentor)
R: Incorrect patching.
P: Your computer crashes when playing videos.
R: There is probably a broken Codec.
S: Install a graphic driver that is up to date.
P: Textures look weird.
R: Incorrect graphic settings.
P: Bugs in LoD, Fc, Ic.
R: The Game is probably using a later graphic engine that isn't working with certain graphic drivers.
S1: Change graphic to OpenGL.
S2: Change compatibility to Windows XP (right-click on Nostale -> Properties/Settings -> Compatibility)
S3: Install a later graphic driver. You can find one on the homepage of the provider of your graphic driver or your notebook.
S4: Activate AAA (Adaptive Anti Aliasing) of your graphic driver (Control panel/Catalyst Control Centre)
Thanks to Unsichtbarer and many other people who created this guide.
You can find the original thread here: Nostale Problemguide