I never read any message as you shared. Here's what you wrote -> "the activation period has expired".
Maybe it said something else?
The full version is not going to be an issue here. Try this first. Click on the Orb or Start button and see if there is an "Activate Windows" item showing. Do that.
As to what you bought. The retail full versions are easy to identify. Fairly big box and all.
I have a PC purchased with Vista and bought what I thought was a full version of Windows 7 Home Premium(Not an upgrade or OEM version) to replace Vista. The PC died and I insatlled a new motherboard. I thought I could use my copy on the new motherboard but Windows tells me the activation period has expired and I have to purchase a new copy. Is this right; Has the licensing changed in Win 7?