Can you describe in more detail what happens when you try to run Mathematica?

I would first try to remove the configuration files (http://support.wolfram.com/kb/12464). If you have not tried already, completely uninstall Mathematica (http://support.wolfram.com/kb/12473), download a new installer and try installing it.

If you continue to see problems, you should contact wolfram technical support (http://www.wolfram.com/support/contact/), letting them know what you've tried already.

I tried all of those and nothing worked. I ended up contacting technical support and they told me to try to boot it up in safe mode. It worked and when I went back to normal mode it also finally started working.