CPU Usage Rockets! 40fps in Doom III lost!

hello PCers
my athlon 64 3400 processor has for four years run idle(no apps running) at %0 to %4 CPU Usage when I check in task manager. I've got this documented from tests I did at PCpitstop.com plus it's just something I check pretty often out of habit. Today, out of the blue, my CPU Usage is idle at %30 to %60... NO applications running! it irks me greatly. I've erased all temp, recycle bin files and defraged, searched for suspicious processes, and run ad-aware to no avail.

little tidbit, i just installed and ran Second Life for the first time last night but it seems pretty good about only running when it's running. It doesn't seem like the problem to me but likely could be related.