Possible virus?

I have a problem that I am not sure, but think it may be virus related. I (actually my sister-in-law) has a computer that worked fine until about a month ago. It is a dell desktop, running Windows XP, SP2. About a month ago her desktop could no longer access the internet. There is a DSL modem and wireless router that works with two notebook computers.

Under the network connections in Control Panel, there are no connections shown. It appears as though something has deleted some windows files, and I cannot seem to get them back.

My concern is also that the computer seems slow, and some other programs no longer work.

Since I cannot get to the internet from that computer, I will need help checking for viruses via programs that can be installed via USB drive.

Any ideas of where to start??

Thanks!

Download OTL by OldTimer to your Desktop.

• Close all windows and double click OTL.exe
  
• Click Run Scan and let the program run uninterrupted
  
• It will produce two logs for you, one will pop up - OTL.txt, the other will be saved on your Desktop - Extras.txt. Post both logs in this thread.
  
• You may need to use two posts to get it all.