Windows internet explorer 7 problem/windows problem?

for some reason, i went to this one site and it had all this pornographic stuff on it, so i left. then i turned my computer off then back on the next day, and i had all these antivirus system pro alerts saying "you computer is being attacked by an internet virus..." and then saying "do you want to... show more for some reason, i went to this one site and it had all this pornographic stuff on it, so i left. then i turned my computer off then back on the next day, and i had all these antivirus system pro alerts saying "you computer is being attacked by an internet virus..." and then saying "do you want to block this attack" and i say no since i dont want to pay for it. i also have this spyware alert that keeps popping up.

the most annoying thing is that internet explorer keeps popping up by going to random porn sites and viagras site and i dont even click on internet explorer.

can someone please tell me how to fix this and/or telling me how i can get internet explorer off my computer?
Update: thanks for all that help, but now i cant even sign on. it says "This system is shutting down. Please save all work in progress and log off. Any unsaved changes will be lost. This shitdown was initiated by AUTHORITY\SYSTEM" and i cant even close that message. so what can i do to fix this problem... show more thanks for all that help, but now i cant even sign on. it says "This system is shutting down. Please save all work in progress and log off. Any unsaved changes will be lost. This shitdown was initiated by AUTHORITY\SYSTEM" and i cant even close that message. so what can i do to fix this problem to fix the last problem
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