I purchased a Microsoft Surface Win 8 Pro last week and activated my windows 8 online. I tried to upgrade to Win 8.1 as given in the User Guide provided in Microsofts Website. I searched to Upgrade in Windows store and I did not get any application in App store to Upgrade. After a continuous search in Google I got an application to upgrade to Win 8.1 and I downloaded to my system. I ran the application to upgrade my win 8 to win 8.1 and it asked to activate windows. By mistake I pressed "yes" and it changed my OEM product key. Then I restored the surface to factory default setting to recover my OEM product key back but it was failure. The new key is appearing every time. I contacted microsoft support team to guide me to get the OEM key back but they informed me that "OEM Product keys are pre-injected in the device and they have not any record of this". Can anybody help me to recover my OEM product Key ? I will be very thankful to you.