Complete shutdown

I downloaded Avast! home edition and updated my program. I try to scan my hard drive and the thing shuts itself down. I can’t find any reason or log that tells me what happened. HELP!

What exactly does it mean “shuts itself down”?
What operating system do you have?

I run on Win XP. When running a thourgh scan the computer shuts off. Dead I have to restart.

Its probabily:
1-Your Hard Drive is Damaged by Bad Block
2-Aplication Conflicts.

Please, turn ON your computer, in the black screen about your computer and BIOS, hit F8 key several times until the security mode option appear.
In the Security Mode, run avast scan.
If your computer shutdown, is a possible Hard Drive Damaged, and your computer not shutdown, possible programs conflicts in the normal mode with other antivirus, antispywares, etc.

Goodbye!

Shuts off, as a bluescreen?
What is your System failure setting? (System Properties / Advanced / Startup and Recovery - Settings / System Failure)