Hi cshajkur
You have only just posted a problem without much detail, so it will take a few messages back and forth to help resolve it.
Please, if you have any AV installed, uninstall it.
then reboot.
then download and run this program.
http://www.avast.com/i_idt_1336.htmland follow it's instructions.
Shut down ALL running programs.
Then try re-installing avast4 and make note of where it stops.
Then please post here quoting what the install program says when it stops as that will help.
Please also post your system config. Operating system, memory etc.
The more detail you supply, the better the chance of someone being able to help.
Cheers
w0mbat