I updates from windows 7 to windows 10 yesterday, and decides to get back to 7 today
Your best bet is to do a wipe and reinstall. You can reactivate your windows 7 with the key on the label somewhere on your PC chassis. It will tell you it has been used, but you need to use the activate by phone method. If you don't have a W7 CD or boot drive I can tell you how to make one. You will need an 8GB flash drive to do it.