Monitor problems

I took Windows XP off my computer and loaded Win98SE. My monitor only shows 2 color choices: 2 or 16. The resolution is poor. Is the problem my monitor driver or the video card driver? I’ve used the same boot floppy and cd-rom (with Win98SE) before and it always worked fine. This is a new Dell computer and it came with XP os. Any help would be greatly appreciated. I got a virus on the computer shortly after I got it and I did a system restore (in XP) but it’s never been the same since. Thanks