By excluding the file/s not the drive which would leave a gaping hole in your security.
Telling it to do nothing just tells avast not to take any action (move, delete, etc.) but it won't allow a suspect/infected file to be run.
What is the infected file name, where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (right click the avast 'a' icon), Warning section, this contains information on all avast detections.
What is the purpose of these files ?
Add it to the exclusions lists:
Standard Shield, Customize, Advanced, Add and Program Settings, Exclusions (right click the avast ' a ' icon)
Exclusions should only be done if you confirm that the detection is false.
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner and
report the findings here. I feel virustotal is the better option as it uses the windows version of avast (more packers supported) and there are currently over 30 different scanners. You can't do this with the file securely in the chest, you need to extract it to a temporary (not original) location first, see below.