virus program causing fatal excpt.

on other computer, we finally got it back up and I loaded AVG this morning. Now the computer won't start windows, VDX AVGCORE keeps causing fatal exception. Can't get past it. I went into DOS, but there is no uninstall program. Is there a way from DOS to delete this file, or the folder and maybe cause this to go away??
and this is the same computer I've had soooooooooooo many problems with. If you kept having blue screens and fatal exceptions right and left would you first replace the harddrive or the motherboard?? cause somethings got to go!