I had a system I posted about a couple of months back, but I solved that one by adding new thermal paste (used MX2, and put more than they tell you to use) and also no longer playing ps2 games, which the system did not like.
This is a different system. It has not gone full blown YLOD but it is doing random red blinking light shut-offs. So far I have:
1) put new thermal paste
2) swapped the hard drive
3) swapped the power supply
4) swapped the fan
Sometimes the system won't stay on for more than 10-20 seconds or a few minutes. Sometimes it will stay on for hours (chilling in the menu). It's the inconsistency that's driving me nuts and making it really difficult to diagnose. The guy I'm trying to fix it for stated sometimes he could get 20-40 minutes of gameplay, and sometimes hours. I only ran a blu ray last night but didn't get more than 1-2 hours before it shut off.
Any ideas? I really don't want to re-flow it if it's not GPU related. It sounds like it could be a system that is on the road to YLOD, but if it's a completely different issue re-flowing it will not solve the problem and possibly make it worse.