Starting to get random, hard lock-ups/freezing

A couple days ago I started getting random, hard lock-ups where everything would freeze, no BSOD. I had to restart my computer manually. The freezes do not happen that often. Sometimes two days apart, sometimes one happens, I restart, then it does it again. At first I thought maybe it was the TLB erratum rearing it's ugly head so I enabled the bug fix because I have been running with it off. But, it still had a hard lock-up after I enabled it. I don't think its overclock related because when I was testing overclocks, I would always get a BSOD when I found a setting that did not work when testing using something like Prime. I have noticed that it tends to happen when I am browsing using firefox. I have never had a hard-lock using anything else such as games, 3dmark, etc. I do think my AVG antivirus may have locked it up one time, not positive on that one.

Any ideas? I am currently running MemTest on that computer in question while typing on my laptop.

Memtest was fine, no errors. I'm running a Phenom 9600BE at 2.7ghz, 1.4volts. My overclock runs prime95 for 8+ hours no problems. That is why this is weird to me. I would think if it was going to lock-up, that would be the thing to cause it. Not browsing with firefox. I reinstalled firefox so all I can do is wait and see. Its frustrating that I cannot figure out how to replicate the lock-up and then find a solution from there. Also, I have the TLB fix enabled.

I seem to remember the fix for this was to ungang the dimms, or was it gang the dimms? .

Just to give a little more detail, when the lock-up happens, I can still move the mouse cursor around for about 10 seconds, but clicking on anything at all gives no response. That is how I know it is about to happen. Like I will be scrolling through a web page, and suddenly it stops. I'll move the mouse cursor around, even try the start button, but nothing. Then the mouse cursor locks as well, and I need to manual reboot.

Was hoping for some more insight.... Anyway I just reinstalled Windows 7 because I was still getting random lock-ups. I am hoping this does the trick. Any chance it was a corrupt registry that would cause my problem?

This may not be the source of your problem but I had a Microsoft optical usb wheel mouse that was defective.Most of the time it worked but there was something defective in it like in the wiring.The red LED light would shut off and then the mouse cursor would completely freeze up.It acted that way on other PC's as well.I took it apart to see what was wrong (like perhaps a solder joint became loose so I could just re-solder it).I didn't find any broken joint so I just threw it away and used the other one I had.Never had a problem with that one.