I have a homebuilt spare PC in the bedroom and when it's on it sounds a bit like an airplane (loud).
One of my favorite features of windows that many people don't seem to take advantage of is "Standby Mode", which basically puts your PC into a very low power state, very quickly, that it can very quickly wake up from. It's a great alternative to shutting down and restarting if you just want to turn your PC off for the night, etc.
I noticed recently that my PC stopped going into a silent
standby mode, for no apparent reason!
What was the cause? How to fix it?
Well, it turns out that there are at least 2 different kinds of Standby modes (S1 and S3) that a PC can go into. S1 leaves the fans and usb connections on, S3 turns off the fan and usb (this is the quite mode)
And there are several things that can control whether your PC goes into S1 or S3 standby mode.
For me, the answer was to go into the bios and change the bios power setting to "S3 ONLY" mode.
There is also a registry setting that addresses this issue, though it's not clear to me whether you should set this INSTEAD of the bios setting, or in addition to.
For a longer description of related settings see this nice post on the matter: http://thegreenbutto...ms/thread/29899.aspx
From your bios you can also do some nice stuff like configure your power button to go in and out of standby mode. For a spare bedroom PC this is a great setup -- push the button at any time and the PC wakes up or goes to quiet sleep in seconds.