I've seen a LARGE amount of users who upgraded that cannot activate Windows 10. I've done some research, and this is currently an issue with the MS servers. Just be patient. Several have decided to just wait, and they have finally activated Windows 10. Just hold fast.
Also, use this thread to post your specific issues. Mine was 0xc004f034. Server issue. I'm still waiting, but I also notice everything works fine without activation... No watermarks or anything.