something strange..

hi everybody..
i have a strange problem which i cant know what's causing it..
am running kaspersky + spybot search & destroy and a firewall on my laptop.
but 2 days ago, and suddenly the laptop turned to be too slow without doing any action, nor visiting any strange link or installed anything suspicious, nor accepted any file from anybody.
the cpu usage is goin high while doing nothing, on the task manager nothing seems to be having anythin from cpu usage, i ran hijackthis, but i guess i havent find somethin suspicious also.. it's driving me mad coz it was working fine, and suddenly this happened and my laptop turn to be slow, and even the windows welcome sound track doesnt work in 1 time.. :S..
can some1 plz give me suggestions, hints or anythin ?!
thanks in advance..

regards

 

thanks for the reply m8..
i already did these steps which u mentioned, and i know that my problem might not be related to malware or something, and i did run registry cleaner and the Ccleaner, plus the start up things on msconfig.
i didnt know where to post in case this wasnt malware related thing :/
but it's so so strange to happen this way. the cpu usage is high while doing nothing, even running a song, doesnt play properly, and my laptop turned slow suddenly, and it's too hard to judge what's happening.
some1 told me to remove windows updates from control panel. i dunno if this can make anythin better, but i guess it has nothin to do with what's goin on :/.
i dunno what more i can ask for help :S
thanks in advance.

regards