Your last post made me laugh, brought back memories - the panic attack when it won't boot, the swearing to the computer gods that if they just let it boot I'll never open the case again! The flood of relief when it finally lights up the screen.....actually, I still have those moments every now and then, like when I overclock too high and after the BSOD it can't find the boot drive. And RAM still fails to seat for me sometimes, and it takes 2 or 3 tries to get it working. Nobody really knows why this happens, but I suppose that memory modules are very sensitive to electrical resistance, and even a little dust in the slot or oxidation on the contacts can cause the problem. Last week I had the same problem with an old DDR2 module, and after lightly buffing the contacts on the module with a scotchbrite pad, it worked fine. Glad I could help, you're now practically an expert in the art of DIMM installation....