I had a serious virus on my windows xp pc last month.
I tried to remove it with everything I could think of, but there were a lot of registry keys that were affected.
The antivirus and antispyware removed them, but they were still there when I rebooted. I deleted them manually, but the same thing happened.
What finally saved me was installing Comodo firewall. It sandboxed the applications that were trying to run, and blocked the harmful registry entries. Then I did a couple rescans with the antivirus and antispyware, got rid of all remnants and rebooted. Now it works perfectly.
TL;DR: comodo firewall + malwarebytes + avira or avast = saved me.
They are all free products.
here’s the link for the firewall https://personalfirewall.comodo.com/free-download.html