That will be hard!! The cmd stays opened like a second or two. Anyway... I've studied the TaskList and realized that two processes were created when the 100% CPU Usage started. So, I started looking which one was the second one.... and I found that the file is net.exe

Holy c**p!! Wouldn't be a virus?? I'm scanning my system now, and the stupid antivirus (who should have been resident avoiding the infection) says that the WORM/NIMDA.E was found in dozens of files.

I'll let you know the results... and if this was the problem.