Dual Boot Up

I recenlty installed win 200 pro on my win 98 se.
It was working fine for 3-4 days but now when i am working in win98 my pc suddenly restarts and it also doesn’t start properly. It hangs at start up after pressing reset key 3-4 times it hardly starts.

what is the problem ?
If i want to uninstall win 2000 pro How to Uninstall ?
thanks