problem re registering

[nilmot]

switched on computer,yesterday, to find windows security alert informing me my anti virus protection was out of date.np got a new key,entered it as per instructions still telling me i have no protection.have noticed reg key no has not changed when i right click on a icon and click about avast still shows original reg no can anyone help please?

[Lisandro]

Which avast version are you using?
What happens if you uninstall, boot, install again, boot and insert the new key?
Are your system time and date (specially month) correct?
Did you use the trial period or just the Home version?
Are you using any other antivirus in this computer? Did you have one - besides avast - in the past?