First - What avast processes are running in Task Manager, they begin with ash or asw, see image ?
Try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow.
Well avast wouldn't have any association with the request to rename the computer (I suggest you try a google search for that), so there are other issues going on, possibly the system is infected. So you could also try these tools, see below.
Have (or did) you another AV installed in this system, if so what was it and how did you get rid of it ?
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If you haven't already got this software (freeware), download, install, update and run it,
preferably in safe mode and report the findings (it should product a log file).