EMERGENCY: My laptop keeps shutting down randomly, how do I stop it?

I tried to download ad-aware after I got infected, but it will not let me open or download ANY antivirus software to quarantine or remove this spyware virus. It just keeps giving me popups that say I have been infected would you like to activate your security software and then ads like Viagra will appear. I don't know what to do since I cannot download and run an antivirus to remove this! PLEASE HELP!

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