Win XP, Hi memory usage with explorer.exe

Hi all,

I am having a problem with explorer.exe in my task manager. Every time i
open a folder with mpeg and avi files, my memory usage with explorer.exe
shoots up to 99 % and remains there for 3-5 minutes after i close the
folder.

I did not have this problem before, but then i download a file that had a
trojan in it. I have norton antivirus and internet security on my computer
right now. I don't think i have the trojan anymore since i used spybot, and
a couple of other anti viruses to find the trojan and remove it. Somehow,
none of the antiviruses located the trojan. I also did an online scan with
Symantec and no virus was found.

I have tried for weeks to figure out what the problem is and even ended up
formating my hard drive and reinstalling xp. But that problem still
persists. I have an 1800 xp system with 512 ddr ram and my virus definitions
are up to date.

Does anyone have any idea what the problem is

thanks

ap