Computer restart issue with avast

Hello,
I recently downloaded avast! free version 6.0.1289 and while the scan/remove portion of it seems to work, I ran into a different issue. Everytime I start my computer, after around twenty minutes of working normally, it restarts itself - and when the system boots up again, avast! is switched off.
I don’t mean to imply this is an issue of the program itself, which I have been using on several previous computers without problems, but I find this particular connection - of the auto-restart and avast’s shield going down - rather interesting. I honestly don’t know what’s going on there: anyone here encountered a similar problem?
Thanks in advance.

I recently downloaded avast! free version 6.0.1289
what AV did you have before you installed avast ? did you remove it before installing avast ? have you run a removal tool to make sure any leftover files are gone ?

run and reboot - Uninstallers for Security Software
http://thewebatom.net/uninstallers/security-software/