Is your powerplan running at HIGH PERFORMANCE? on a desktop you shouldnt have the option for anything else..
I have seen "unknown" many times in my troubleshooting, usually in startup programs, and in services.
In most cases its been virus,malware,adware,or hijack related or even registry corruption.
I know youve done a virus check, but have you run Spybot search and destroy? It finds things that are not usually searched for by antivirus programs, and does an awesome job finding and removing stubborn malware and browser toolbars.. Version 1.62 is the better version. Ver 2.0 is too heavy on time with no extra benefit..
If your powerplan is not set at high performance can you type the following command to make a copy of your powercfg settings
from the command prompt its powercfg /query >>c:\mypwrcfg.txt then upload that file from your c:\ directory..
only your powerplan settings are in there, there is no personal info or system info in that file, its a txt version of your powerplan config.
If its not your powerplan and not a virus/malware maybe your power is glitching.. Is your system on a UPS, maybe the power supply on your desktop is failing...
[DEL]Does your system have to sleep or can you put it in hibernate instead? Does it need to do things when youre not there?[/DEL]
Its ironic that your system wont go to sleep after being awakened, and another member on this forum has the opposite, his system wont stay awake after wakes it up.. I asked him if it was a narcoleptic..