I have seen a lot of malware causing this problem lately. Open your task manager and start ending tasks of suspicious processes. If/when you finally get into Windows try and do a system restore to before you had this problem.
http
/www.bleepingcomputer.com/tutorials/windows-8-system-restore-guide/
If for some reason you can't do a system restore, here is an adware removal tool that has been working really well lately:
http
/www.bleepingcomputer.com/download/adwcleaner/