P4PE motherboard, Windows Vista, and Sleep Mode?

I just did a fresh install of Vista Ultimate on a P4PE-based box I have. This box has run XP and, more recently, Windows Server 2003 for me for a long time w/ virtually no issues at all. Vista seems very stable right now, so I'm pleased with that.

The one thing that's not working as it used to is when I put the OS to "Sleep". Everything shuts down but the power supply fan keeps running. I've let it run for many hours, and it never goes off.

Searching google and elsewhere, I've tried every tip I've come across: upgraded to latest bios; turned off usb keyboard / mouse from bringing box out of sleep; registry tweaks from a MS KB article; etc. Nothing has made the box less stable, but the power supply fan just keeps on running.

The only thing I'm not sure if I've tried correctly is configuring the bios power mgmt settings. I've seen some pages mentioning it should be set to "S3" and if it's set to "S1" I might see this behavior. However, I don't have any settings in my bios power mgmt screen labelled "S1" or "S3". The way it was configured worked under XP. I've tried one change in those bios settings, but that didn't help.

Any thoughts on the right way to get this fixed. I've got enough PCs running in my office that if one's asleep, I'd like not to have the noise from a fan (even though this one is pretty quiet).

Thanks much,

Donnie