I don't know what oem even is. I bought the windows 8.1 64 bit that was the most popular. now a Microsoft tech said I cannot use an oem version for my new pc build that I need a retail cory. I thought that's what I bought. I also bought a flash drive since I wont have a disc drive on the new pc. I don't get the case til Monday so I wanted to put my copy of windows onto the flash so its ready. What am I to do now? I still haven't opened it.