Video Problems

I went out on a call yesterday with a guy who’s computer wouldnt boot up in win98. I SYS C: ‘d him with a boot disk and it was fixed. However when it boots into win98 video won’t go past 16 colors and the resolution won’t go past 640 X 480. Everytime I set it higher, the system reboots and when it starts windows there’s nothing but a black screen.

To fix it I have to go into safe mode, set the adapter to default and its fixed but it’s fixed at 16 colors and the same res.

Any suggestions on how to fix this?