file in use by another program, can't open msconfig, regedit, taskmgr

first run a virus check, if you don't have norton or anything else there are lots of online scanengines/
second, run several anti-spyware programs like adawre, spysweeper, microsoft anti-spyware, they are all freely to download on the internet.

Yeah, sounds like some malware (malicious software)

What I recommend you do, is download the following two anti-virus/anti-spyware software:

   Anti Virus:      AVG                       ->  http://www.grisoft.com/doc/1
   Anti Spyware: Ad-Aware Personal -> http://www.lavasoftusa.com/

Then, boot up into Safe Mode, like so:

Reboot your machine  ->  and as soon as it first starts loading (ie, the power restarts, etc) start hitting the F5 key (although it sometimes changes with different machines - check your documentation if this does nothing).
From there, you need to choose to boot into Safe Mode, etc.. Then you log into the "Administrator" account (it should make more sense when you actually get to it).

Once you're logged into the "Administrator" account in Safe Mode, run AVG and then Ad-Aware. Remove anything they find  ->  then just reboot your machine, and cross your fingers.  ;)

Regards;

Maybe this is usefull too:

Download HijackThis from here, run it and Save the LOG file >> http://www.merijn.org/files/hijackthis.zip

Then Post that log at this site >> http://www.hijackthis.de/en

hit the Analyse button, scroll down to the bottom, hit Save Analyse link, a new page will open, just post here the address of that page!

Tolomir

Thanks! I've been running some anti-spywares and antivirus with no luck, I think I could detect the malware if I could have access to the list of running processes, but I can't start taskmgr.

Do you know another way to see and terminate running processes just like with taskmgr?. I've been searching for a free utility to do this, but I have found nothing.

Check this page out for info related to your problem:
http://windowsxp.mvps.org/ToolsQuit.htm

RF

Using procexpnt I could detect the malware and delete it (it was a file named like MSN messenger).

Thank you Tolomir, and thanks to all who participated!