It could b becuse of spywares.
If it isn't then try multi tasking ur pc to the greatest extent possible. open about 20-30 windows, photoshop, encode etc ti;; ur pc freezes.
Now wait for some time and then restart.
Ur processor utilization should come down now.
I do it once every month.
If u think u can even get the logic behind it.
P4 1.6GHZ Willamette core 400MHZ FSB 256KB L2 cache
Intel 845WN Mobo
Nvidia Riva Tnt2 M64 G-card
40GB Seagate 5400rpm HDD
15 LG Studioworks563N
Creative Inspire2400 2.1 speakers
16x DVD ROM
52x Samsung CD Burner