My computer has a virus! HELP !?

[bishvabis]

So, one day I was on the house computer, & this virus protection thing popped up saying I had x amount of virus's and I needed to download the virus protection, but I didn't 'cause I've always heard if something pops up saying you have a virus, that's the virus itself. It won't let me open my virus protection to get rid of it, and it wont let me on the internet and I've tried F8, that won't put it in safe mode. Help, please & thank you!
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mother board