I installed Avast! Internet Security 30 Day Free Trial on Wednesday 8/26/2015. It expired a day later on the 27th. I have not changed the date or time info on my computer, so I don’t know why it went out.
Have you previously used the trial version or uninstalled it at any point ?
Try an avast repair - Control Panel > Programs and Features > Avast Antivirus > Change - Scroll down to Repair. Reboot when the repair is complete.