pc slows down when connected to network

Hi there! I have a dell with a windows xp os that was working fine
until a couple of weeks back. The problem is that it takes almost
forever when I try to open any file (.pdf, .doc, .txt, etc). However,
there is no problem when I try to open individual folders or when I
try to drag and drop the file into the related program. Everything
works fine when I am not connected to the network. All help is much
appreciated

Are there errors listed in your event log? I would also look for spyware
running on your machine.