How do I rid all the viruses on my HP Laptop?

Well as the title says how would I get rid of the viruses on my computer. I’ve already cleaned my computer out and reinstalled all my programs again, but I had a feeling they would still be on my computer… I have microsoft essentials as my antivirus software. And before all the viruses I had excellent protection, if that makes sense. But i just want to know how do I get rid of them. I’ve looked on google and that didn’t do much…. Just told me to buy antivirus software, which I didn’t want to to do. Also, my laptop is currently shut off. I’m using my mom’s desktop to post this question. Help?