before u panic..
actually, here's what u do.
disconnect from internet...if still no change, that means ur not being hacked.
Look at your taskbar, it can be a virus scanner scanning, a scheduled task like Defragmenter working,
or another program.
on the other hand, if u think someone is accessing your system, go to Start, Run, and type in "compmgmt.msc" and Enter.
Under SystemTools, SharedFolders, you should see Shares, Sessions, OpenFiles...click on these to make sure things look alright.
if someone is accessing your files, it will also show up there. Sessions and OpenFiles should 'usually' be empty, unless someone IS
looking at your files. You can also do a few other things like turn on full logging under your Profiles, to audit access events etc...
then you will be able to see any activity in your EventViewer(Start, Run, "eventvwr" and Enter).
a personal firewall with IDS is also recommended...