Going off of memory since I'm at work:
CPU: AMD FX-8120
RAM: Not sure of models, have 1GB(x2) and 4GB(x2)
Motherboard: GA-970A-D3
Video Card: GTX 260
PSU: not sure of make/model 600w
Not overclocking, system has been running for over a year. I have the settings in to BIOS set to warn when temperature gets too high, currently set at 90c. About a month ago, the temperature buzzing started warning me while playing a game. Checked it out in HWmonitor, TMPIN2 (northbridge) was the one overheating.
I have cleaned the stock thermal compound from the heatsink and reapplied some new thermal compound, and it ran fine without overheating for a few days, then would start overheating whenever I run a game.
I cleaned the heatsink again, and reapplied thermal compound, this time it worked fine for two weeks. I touched the heatsink when it is idling around 70c, and it does get warm, so the heat is transferring to the heatsink. I took the side off of my case and rigged a 120 mm fan to point directly at the heatsink, ran prime95, and it started overheating within a few minutes.
Does anyone have any suggestions?