ECS mobo Intergrated Graphics Yellow lines/Freeze

I built a computer for my buddy about two years ago and he suddenly had a strange problem. Out of nowhere his computer would get BSOD or the display would go bizarre and show yellow artifacts/shadows over everything and freeze. I took it in and first decided to check out the southbridge of the chip since I believe that's where the whole IG are, right? After 10 minutes of warming up I give it a feel and almost left a bit of my skin on the chip. It was painfully hot. I checked temps with HW monitor and noticed something was around 55~60C.I had an old cheap aluminum heatsink that I put on and noticed the temps drop to a much better level, in the 40's. So I figured this must be the problem. I glue the heatsink on and ran ATItool for 15 minutes, smooth sailing and the new heatsink was luke warm. I figured problem solved. My buddy takes it and I tell him to let it run for a bit to break it in and see if all goes well. We go out to eat and hang for bit. When he gets home about 3~4 hours later he has the same exact problem with the yellow lines. I told him to call me if he had any problem ( I really didn't expect it.) My next test would be to throw my video card in and disable the onboard and let it go overnight. I guess if no artifacts appear its safe to say he can pick up a cheap PCI-E card. Any suggestions, thoughts, comments?

Well, I think I found the problem, not sure why or how it was caused but I will explain. My friend dropped it off back at my place for me to check it out again. I go plug it up and power it up. Unfortunately it gave me the infinite beep during POST. So I figured....huh this can't be all caused my bad memory..or could it? How does bad memory cause artifacts? Any who I install some spare memory I had laying around. I Blend tested it for 6 hours. Now if you remember the computer locked up just idling for roughly three hours at my friends house. And here we are passing a prime blend test for 6+ hours. This seems promising. So to verify if the original memory is a problem I plug it back in. Not before cleaning off the pins with some rubbing alcohol and a Q-tip. Just in case. This time I had it on all day, half the day running prime, the other half scanning for viruses etc just for fun. No problems. I did however put the memory in another available slot. Not sure if that was all the difference in the world or not. I doubt it since I believe memory would 'break' before an actual slot would, but hey anything is possible and I really don't have a true explanation of why it works fine since nothing has really changed. Possibly the memory fell out of place from the transportation and cleaning and reseating it may have fixed it.