I should wait with reinstalling OS utill trying at least two things:
1: You mentioned that svchost.exe was taking up a lot of your cpu power. A common worm (msblast) infects this file. I'm not sure you have it, but I would recommend a check-up.
2: Read your mobo manual carefully and check your bios settings. Most bioses has some settings for the cpu, changing them did the trick for someone else with the same problem (and me many years back
). Removing the battery on you mobo, and shorting 2 specific pins (differs somewhat from mobo to mobo) will restore the default settings for your bios. which pins? read your mobo manual!
If you don't have your mobo manual, check your model name (printed on the mobo) and search for the manual online.