If it is in the chest, it can do no harm there, provided it isn't still in its original location (as you said it has been detected twice, so it could be coming back) then you should be OK to install SpywareBlaster.
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 icon), Warning section, this contains information on all avast detections.
Not all infected files can be repaired. The VRDB only protects certain files, .exe, dll and other system files, it doesn't protect data files or all files, it is not a back-up program, so there are going to be many occasions where repair won't be an option.
Only true virus infection can be repaired, e.g. when a virus infects a file it adds a small part to it, provided that file is one that avast's VRDB would monitor and you have run the VRDB, then it may be possible to repair the file to its uninfected state.
However, for the most part so called viruses, trojans (adware/spyware/malware, etc.) can't be repaired because the complete content of the file is malicious.