Was running fine for months with 4x1GB of PC6400 Ballistix ram in a P5K Deluxe.Then a stick went bad, the store quickly replaced the pair.The new Ballistix ram looks somewhat different has a different heat shield, but its still PC6400.But now my system has random crashes with 4GB installed,yet either pair with just 2GB installed is fine.Any ideas?

Back when I built my AMD3600+ to run FS2004 with 4x512KB of RAM I found it would freeze after a certain time. Pulling out 2 of the sticks fixed the problem. It still works fine now with 2x1GB.I recently bought a highly overclocked Q6600 machine and the suppliers declined to fit extra sticks of RAM because of potential instability problems.So, 4 sticks should work but sometimes don't. As George Orwell might have said, 2 sticks good, 4 sticks bad :)--Bryn

Seems common another just did the same.I swapped the new pair again and so far I'm running with 4x1gb installed again.maybe as teh ram prices reach all time lows quality is too?

While running 4 stick of any RAM, it may be neccessary to loosen the timimings a bit in the BIOS. Especially the command rate from 1T to 2T. Also, make sure the pairs of sticks use the same voltage rating (label on the sticks) and set it accordingly in the BIOS. That's where I would start.