Vista security pc center licensing

so basically my aunt has a lap top and she got a pop up on her desktop saying her security is out of date. She can't acces her start menu and to access the task manager she has to ctrl alt del. i kno it is a pop up/virus since it is indicating it has soo many vulnerabilities and dangerous things. how can we get around this without reinstalling vista.. and when she goes to cancel it it says action can not be completed. or something like that.