Can you access anything, or is it getting stuck while trying to boot up? If you can open the start menu, you should be able to to to Settings, then click on Update and Security>Recovery. If you can get to this point, you can revert to Windows 7.
Ok, then I would try to boot into safe mode and restore Windows 7 from there (assuming that's what you want to do). Unfortunately this can be a little trickier on Windows 10 than Windows 7 or 8. Tom's Hardware has a good guide on two ways to do it with Windows 10 - http://www.tomshardware.com/faq/id-2569556/safe-mode-windows.html