After you follow Bill's excellent advice, the below may help.
You are lucky you can get to Safe Mode, at least we have something to work from.
So if safe mode is available try SAFE MODE Networking. This will allow you to access the Internet and download the below.
Do some cleanup. Download and install and run these:
The following are the best free cleaners below
Finally **** CCleaner get the slim version http://www.ccleaner.com/download/builds.aspx
Dcleaner and ATFClean are purely disk cleaners but CClean also has a registry cleaner (issues), run this also as many times as it takes to come up clean.
Now try a normal boot.