If your computer has been able to run the game in full-screen mode before, then it should be able to again, as long as you haven't made changes to your computer that caused the problem. Such things as updating drivers, installing new hardware or software, or altering settings on your computer can affect a program's ability to operate properly.

Have you gone through all of the troubleshooting procedures in the first post in this thread to make sure that all of your computer's settings are set properly? If they are set correctly and you want to try full-screen mode again, you will need to change the configuration file so that it no longer forces windowed mode.