"Parity" means it is a memory error of some sort, though the exact cause isn't immediately obvious.
1) Check to make sure all your RAM is the same speed/type (all ECC/non-ECC, for instance).
2) Make sure your RAM is distributed amongst your memory slots the way your MLB manual recommends.
3) As mentioned above, check capacitors (the little metal cans) on the motherboard for any
signs of failure.
4) Start pulling out memory chips and testing to see if you can isolate which ones cause the machine to crash.
4b) Run
a memory test to heat that memory up and make sure it is solid (Note: This can take a loooong time)
If all of the above is successful:
5) Try to run something really CPU-intensive to see if the memory causing the error is the L2/L3 cache memory in the CPU itself (which often has an ECC/parity check associated with it).
5b) You can also (usually) disable the cache memory in the BIOS to see if that makes a difference (though this will make your computer
much slower).
6) Start pulling expansion cards out and seeing if you can reproduce the issue. This includes the graphics card (it has memory on it, too!), though I don't know if you would have a spare to test with.
7) If all else succeeds, try a different hard drive. It may be the cache memory on the HDD or possibly the interface itself that's doing it.
I realize I tried to be thorough, but you're actually most likely to have resolved this by the end of step 4 and probably won't need the rest.
--Patrick
