I'm using 64-bit Vista Home It had been running for almost a year on a Gigabyte GA-P35-DS3R motherboard with no problems. That board died so I replaced it with an Asus P5K Premium, and carried out a fresh installation of Vista. Since then I have been unable to put the PC into sleep mode, either by using the power options or by forcing it to sleep with the relevant command from the start menu. The screen goes blank, and I get lots of disk activity, but the computer remains resolutely awake.
ASUS BIOS on recent boards screws over the 'sleep' settings. I don't know about the P5K BIOS, but I tried every setting I had and read hundreds of links on how to fix my 'sleep' issues with my ASUS maximus Formula x38. Finally...and I stress finally ASUS issued a BIOS revision that addressed the Vista sleep issue. No problems since that BIOS revision. That would be cool if OP set up to S3 in BIOS and it worked 8).