Hi, Have you tried mbar.exe antirootkit or aswmbr.exe , which contains the cure for infection in MBR. Have you attempted Boot scanning option in the AVast. Naturally, avast boot scan will kill all the trojan, rootkits, etc before the window boots.
I have doubt, that your virus, if it is virus, gets to your system from the infected restore points.
The mbr fix by reputed avast will do no harm to your computer. It will prompt, if you need cleaning of rootkits or fix mbr.
Once the problem is over, kindly delete all system restore points, which are the main source of infection.
Shane, i think , will approve my idea to you. I have quite a number of uncurable diseases in my computer, which was set correct by avast boot scan, which is a boon to the society by AVAST