Lets try something and see how it goes.
Double-click on the Rkill desktop icon to run the tool.
If using Vista or Win. 7, right-click on it and Run As Administrator.
A black DOS box will show and then disappear (wait for it to go away). This is normal and indicates the tool ran successfully.
If not, delete the file, then download and use the one provided in Link 2.
If the tool does not run, please let me know. Or if it seems to have taken to long.
Do not reboot the computer until you have run the applications listed below, otherwise you will have to run Rkill again.
Post the log that Rkill makes, on your desktop, in your next post.
After Rkill runs see if you can run Avast.
If you can please update Avast and run a boot scan. Post the results.
Weather or not the boot scan runs lets also try ESET:
DownloadESET online scanner
Click on START, it should download the virus definitions
When scan completes, click on LIST of found threats
Export the list to desktop, copy the contents of the text file in your reply
You may not get a listing if nothing is found
Let me know how this goes and post all logs, if any.