i am facing some problem with my laptop since a few days.whenever i try to start an antivirus program it stats but after a few seconds disappers that is automatically stops running.i have avast proffesinal antivirus with f-secure internet security2006.
moreover the windows firewall is not able to detect ane antivirus in my laptop.similarly i have ccleaner, but when i try to start it, it does not start and shows that some file is missing.

First off try a System Restore:

start > All Programs > Accessories > System Tools > System Restore

Pick a date back a few days when things were OK.