Licence Key invalid or Expired

Since September this year I use the avast 4.1 home edition. All the time I got the updates, but since Yesterday the Blue Quadrant is Red and tells me that the Licence Key is invalid or Expired.
On my laptop there are no problems and I use it there for the same time.
The only thin I could find is that the date of my PC was wrong (2007), so I Changed it back, but the problem remaind.
Who can help me with this problem

Im fairly new to the Avast Program…I’m just a novice user, but have you tried re-inserting the license key? Make sure your computer clock is set correctly and try to re-insert the license key. Perhaps that will work. Just a thought! Good Luck!

Paul40, follow Dadid’s instructions.

If that does not solve, can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).

Hi,
I’m also very new to avast! - may be a silly question : have you registered for avast! home and entered the sent licence key - if you still use the trial period key then might be realy expired.
br
Peter

Check if your system date/time are correct first…

Well Thank You for your reactions (Technical, Peter and Dvid),
It runs again.
Before my Question
I first checked the systemdate , it was ok.
Then I tried to fill in again my registry code.

After your anserws
I tried to repair, … it failed,
So i uninstalled the program, reboot, install the version i had, reboot, entered my regestrycode and … Yes it did the job, the update went as it is supposed to do.

Bye.