- What OS are you using? is it up to date?
- What avast! version and VPS file (virus database) number, e.g. 0436-4 (see about avast!)
- What was the filename, where was it found
example (C:\windows\system32\infected-filename.xxx)?
- What actions have you taken to try and resolve the problem?
Trojans generally can't be repaired (either by the VRDB or avast virus cleaner), because the entire content of the file is malware, so it is either move to chest or delete, move to the chest being the best option (first do no harm). When a file is in the chest it can't do any harm and you can investigate the infected warning.
Leave it in the chest for a week or two to ensure your system is stable (just in case), then you can delete it from within the chest.