We can't tell you what to do based on your post, in order to help fully we need more information....
- What Operating System 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 virus name, what was the file name, where was it found
example (C:\windows\system32\infected-file-name.xxx) ?
- What actions have you taken to try and resolve the problem ?
Have (or did) you have another AV installed in this system, if so what and how did you get rid of it ?