You'll need to download and run ComboFix - or get someone with experience to do it for you. It's a trojan infection which can turn nasty - and has possibly infected any pen drives or network drives you may have by adding an autorun.inf which points to malicious code. This way the trojan doesn't even need the internet to propagte itself.

ComboFix download and instructions here (http://www.bleepingcomputer.com/combofix/how-to-use-combofix - in case you can't click through the link, copy and paste).

You'd be well advised to download everything on someone else's machine, and put it on a clean pen drive. Make sure you aren't connected to either the internet or your network (if you have one), then follow the instructions.

Don't even allow ComboFix to download any updates once running, because the trojans are now savvy to ComboFix and can hijack its attempts to update.

One machine I cleaned recently had a trojan that recognised the filename combofix.exe and blocked it from running... I changed it to fred.exe and away it went!