Hi, if your computer came with XP installed, it's almost certainly NTFS. They should also have supplied you a bootable Windows CD for repair purposes. Running this CD will not affect your datafiles because these are non-system files.
However, are you sure this is a virus ? Maybe your mouse doesn't work properly ? I read that Avast seems to be running. So, what happens if you use the keyboard shortcuts ?
For instance, the Windows logo key should have the same effect as clicking on "start" :
does it ?? If so, I will send you a complete list of all the shortcut keys.