computer wont shut down

[TyKoN]

Ever since i plugged in my new usb keyboard and mouse my computer wont shut down normally. it only gets to the screen where it almost shuts down but it just freezes there, i cant even move my mouse. this seems to happen any time i have something plugged into one of my usb ports while im shutting down. is this a problem with some settings in my bios or is it windows? and how can i fix it? thanks in advance for any help