can avast home be run fr bootable cd since my puter won't completely boot up ?

Avast Free Antivirus / Premium Security
1

???

2

No it requires windows to be running or having scheduled a boot-time scan from within avast.

Can you boot into safe mode, keep taping away at the F8 key during boot to interrupt the boot, select safe mode. Once in safe mode you should be able to run avast.

Can you explain the circumstances leading up to being unable to boot ?

3

From a bootable CD you need Bart CD from Alwil. Although the price is a little high to afford.
http://www.avast.com/eng/avast_bart_cd.html