Can't Install Anti Virus, Can't Run Firefox

So my VGA was broken, I replaced it on a computer shop. Somehow, they updated the driver using their external harddisk. At home, I now can't run Firefox. I tried installing AVG, it is installed but I can't run it. Even on the Add and Remove Programs window I can't find the antivirus.

Avast didn't work. I have also used Malwarebytes Anti-Malware but I think it only scans, not removed anything.

My questions are:

1. Is this because of virus or malware?
2. How to get rid off this annoying problem?
3. How to protect myself in the future? What are the good and reliable softwares?


I will appreciate any kind help, otherwise I gotta reformat the whole damn thing.

Thank you.