A problem in Windows Explorer in Vista 50% CPU

Hii everybody
this is my question:
I've installed Windows Vista on my PC a month ago and everything was alright at first
but after 2 weeks it goes very very slow
and in the task manager it shows that the explorer.exe operation is using 50% of the CPU (i have a dual core CPU)
and now i have the same problem on Windows 7 on my Toshiba Qosmio laptop
although i tried everything such as Windows Update.. Repairing.. and Tuning up software but nothing solved the problem
so the only thing that would solve the problem is the brain of someone in this forum
I also have Kaspersky Internet Security 2010 on both of my laptop and desktop
so it's not a virus or worm
Thanks in advance to everybody

Process Explorer is a very good task manager substitute, it may help finding out more specifically what is taking up so much CPU. Feel free to post a screen shot of the Process Explorer screen if you want another pair of eyes on the problem. Keep this thread posted as to what you find out (or what you don't find out ).