Low resolution boot up

I’ve got a Celeron 500mHz, 128 mb RAM, using Win 98se and a 3dfx voodoo 3 2000.
For a good while now my computer will every now and then boot up in 640 x 480 even though I run in 1024 x 768. Now it’s doing the same thing but sometimes when I restart i get a “windows caused a general protection fault” message and it shuts down. When I reboot it boots in Safe mode and I must manually reset all my graphics settings. After doing this all seems to be fine until about 2 or 3 shutdowns later whenit happens again. Any suggestions are appreciated!