Help everytime i try to access internet explorer it says my computer is infect?

Ok so right now im using the same computer but on a diffrent user and its works fine but on my other user it says my computer is infected with viruses,trojans,spyware, etcetera and everytime i try to go to google vistaspyware pops up and says my windows firewall is disabled and when i try to enable it it says i have to put a key in or buy the product for 60 dollars???? how come it is doing this? but on the other user it works fine