Have been using Avast Home version for 3 years now. My current version is 5.1.889. Have been facing problems with Avast since last week. My License had expired last week so I went to the website and registered again. I updated my registration information but within a day Avast said my license had expired!! On next reboot it stopped working completely. I reinstalled the software and punched in the license key again and the key expired again within a day. It has now happened to me four times. 
Attached is the screenshot of the avast registeration section after the 4th expiry message:
Can anyone please help me out and let me know why is this happening and what can I do to avoid it…
Is your system time / day / month / year correct ?..if not adjust and reboot
yes, the date is correct and has not been readjusted. it is configured to synchronize to time.nist.gov
try avast repair and reboot
For a repair of avast. Windows, Add Remove programs, select ‘avast! Anti-Virus,’ click the Change/Remove button from the pop-up window, scroll down to Repair, click next and follow.
did it work ?
On-line registration is very simple and it’s the preferred method for all users of avast Free Antivirus 5.x installed on a computer with standard Internet connectivity.
To perform on-line registration follow these steps:
http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=459
Have already tried it. It doesn’t work…
Take the computer outside and shoot it… ;D
OK, a shot in the dark…
Uninstall avast, reboot
Run CCleaner and clean it good reboot http://www.piriform.com/
Run Eusing free and fix all and reboot http://www.eusing.com/free_registry_cleaner/registry_cleaner.htm
Install again, reboot then use online reg
I reinstalled the software and punched in the license key again and the key expired again within a day.
With avast 5.x there should not be a license key to punch in but instead, there is a license file that you double-click to install.
With avast 5.x there should not be a license key to punch in but instead, there is a license file that you double-click to install.Please find attached the screenshot..
Thanks for your help guys…
I really thought of shooting my laptop but finally settled @ formatting and reinstalling. Hope this trouble does not return now.