They all do it .. It's how it is these days ..What's the point?! lol
Look through Add Remove .. Uninstall anything suspicious or unwanted programs. Lads usually have hidden bit-torrent software. That's how a lot of stuff gets installed.
Check this list for names to look for.
http://www.p2pon.com/...-filesharing-methods/
Delete all temp internet files, cookies, and everything you can in Temp Folders.
Switch OFF System Restore, reboot and do a FULL AV Scan, also with Antimalware Bytes (after updating it) in Safe mode if possible.
If you want to look at all processes to check, download HijackThis and run it, then select 'Scan and save a logfile' Look through that list first for "No File" entries, particularly in Run and Services sections. Don't start removing stuff with it willy nilly tho! You can break Windows with it!
Depending on what's on it, and AV may not be able to remove, so you would have to go the RKill and Combofix route.... like I did with Bez recently.