After installing the Windows 8.1 Preview via ISO, I put the license key provided by Microsoft... Activated it via online. My PC worked better for days than the earlier OS but one time, my PC experienced an unexpected shutdown, when I fired it up, it needed to be reactivated again but the problem here is I can't activate it anymore! Even with the key provided by MS, even I have a internet connection... It says "The Key didn't work, try again another key" something like that, can you help me fix this problem or I might even switch to the earlier OS :(

If you download the ISO, you'll need to enter this product key: NTTX3-RV7VB-T7X7F-WQYYY-9Y92F