I had the same problem which occurred immediately after upgrading from 8 to 8.1. I spent a lot of time following suggestions but what solved the problem for me was I came across a post, which at first I thought was a company promotion, saying that CCLEANER would solve the problem with their registry clean-up tool. And it's free. I downloaded the software and ran the registry cleaner three times (rebooting each time) and problem solved. My disk usage is running along at 5-10% and no more time wasted. I was just about to the point of buying a new computer but have to thank this company for saving me the time and money.