Whew, this is going to be a long one.
Alright, first, what operating system do you have, and what service pack level?
You say that,
still no cure.
How do you know? what is telling you there is a virus, or what are you experiencing that is telling you that? If Avast is saying that you have a virus, where is it? what is the path?
You said that you formatted your hard drive, did the virus appear AGAIN after that? Is it possible that you have an external hard drive with the virus, or the virus is on your network, and spread after your recent rebuild? Did you scan those types of media with avast?
Have you run a boot-time scan?
Have you run Malware-bytes or Superantispyware?
Could you post a Hijackthis log?
Do you have all of your windows updates installed?
Have you tried a Antivirus Boot CD?
We'll just start with that.