What monitor do you have, and what games are you trying to run? I suspect your monitor is too new to support the old resolutions that DOS games use.

I don't think it's a problem with your PC itself. Your video card is almost certainly fine with running real MS-DOS games in 320x200 and 320x240 and all SVGA resolutions.

Try running Theme Hospital and Warcraft 2. These games are 640x480. The intro to Hospital is low resolution though, so you might hear the sounds of the intro movie but not see anything on-screen, but the game is high resolution. If you can get to the main gameplay part and see it running, then it's your monitor that's stopping you I think.

Edit - Grand Theft Auto would be a good one to try as well since it has options for lots of different resolutions.

Are you running the games in the Windows XP command prompt?
If so you may need to use videoprt or winxpfix with that graphics card and/or driver
You'll also need to use NOLFB or NOLFBLIM for games that use the LFB
If you don't have any EMS you'll need to disable or remove the hardware eating up that address space although EMS Magic may work.
Use VDMSound for audio
Use dgvoodoo or solvbe for video but only as a last resort
Use NTVDM only if DOSBox isn't fast enough or if you don't want to dual boot with DOS/9x.

I think that's everything....

I took the GF4 4200 out of the computer, and put a GF 6200 256mb nonTC, removed the old drivers and installed new drivers for the 6200, now it's working normally. Has nvidia removed some sort of msdos support from the latest gf4 drivers?

Read this thread:
patch for WinXP/2000 monitor issues
There is also a post in that thread that links to other threads that discuss the issue.