Open Question: What else could be causing my Playstation 3 to freeze?

Hello,
-I have a 60gb ps3 with the 3.15 firmware,
-It freezes when i play games or dvds or avi files saved to the hard drive, or avi files from a USB or SD card.
-It has been out of warranty for years so I have disassembled the system quite a bit and the problem still occurs.
-Right now, the casing is off and the fan is completely exposed, and cleaned and the problem still occurs.
-I have the Blu Ray drive completely removed and the problem still occurs.
-I just cleaned and reapplied Thermal Compound to the 2 chips/heatsink parts.
-There seems to be no real pattern to the freezing, sometimes a movie will play for a half hour, sometimes for 1 minute before it freezes.
-I have tried simple things like restoring the system, formatting the system, removing the HDD and formatting it, restoring the file system.
-Other than a broken lens and an overheating system, what else can cause the Playstation 3 to freeze??
...While I have the case off, I have noticed that the power supply becomes very hot while the system is on, is this normal?
-I was just able to go online and download the Dante's Inferno demo with no problem, however as soon as I tried to play it the system froze.
Does anyone have any ideas/suggestions?
Thank anyone and everyone for their time