Right i basically have got a virus as of yesterday called "xp internet security 2012" on my dell desktop?

hi there people, as i said i got a virus called "xp intenet security 2012" it automatically downloaded itself to my pc via a link i rekon. now this virus imitates windows security essentials, telling me my computer is basically infected by 30 or more trojans. it also stops me getting on control panel to do a system restore and if i download a legit copy of security the virus stops the download. so here it is on my computer trying to get me to put my bank details in and "validate the copy of security 2012" PLEASE HELP!!!! HOW DO I GET RID OF THIS ANNOYING CRAP??? any help would be greatly appreciated thanks.