I just finished building a PC for a colleague and we both decided to take the Asus P5Q PRO because of the price and features. Everything runs smoothly now except that when I turn on the C-State (C2/C3/C4) setting in the BIOS, the PC freezes every now and then (when idle or without heavy load). C1E is enabled and doesn't cause problems. The CPU used is an Intel E8400 and the RAM is a pair of Corsair 1 GB modules that I had to manually set to 1.9V and 5-5-5-12 timings. First I thought the problem might be caused by drivers, but I also had freezes during the Windows installation or while performing memory tests with memtest86+. As I mentioned, after turning off the C-State option in the BIOS, the freezes no longer occurred and everything behaves correctly (including suspending and hibernating the PC). I also flashed the BIOS to the latest version as of September 25th, 2008 (one from August IIRC). Is this a known problem?