Hi eltharion5, welcome to the forum
Do you have a 32bit or a 64 bit system ?
If you have a 32 bit system, go to https://forum.avast.com/index.php?topic=53253.0 and scroll down to If you cannot Boot the computer and follow the instructions.
If you have a 64 bit system, simply tell that in your next reply.
I will notify Essexboy so he can help you.
Greetz, Red.