Dimension 2400 BIOS Resolution

After playing on Battlefield 1942 (RPG PC Game) my Windows Xp Screen 'shifted' to one side, this was easily sorted out by 'Auto Adjusting' my screen using the buttons on my monitor. The next day I again went to play the game however the resolution of the game has changed and i now have to play in small box in the middle of my monitor instead of full screen which Windows is displayed on. I restarted my PC to see if this would solve the problem however it showed me that BIOS/loading screen is now the same resolution as the game (a small viewable area in the center of my screen). I'am running an XFX nVidia GeForce FX 5200 and have had no problems with it prior to this. Any help would be much appreciated.

Regards,
LDearden