Computer Keeps On Crashing After Getting Some Scripts?

bought a computer 2 months ago from a homebased "tech".worked great at first,then became plagued by increasingly frequent crashes finally crashed so totally it could not power back on. motherboard turned out to be literally fried.i kind of shamed him into selling me another (faster, more powerful) unit for half what he'd been asking for it, and to switch my 50 gigs of harddrive for the its 80 gig HD.within a day it began crashing first thing i noticed was that the script (sometimes in text documents,sometimes in various program windows,sometimes on the desktop)would begin to get all smeary and saggy,almost looking like an alien alphabet.a crash always followed soon after.