Safe mode by tapping keys isn't available I think. Does your keyboard work?
If so, in desktop press the windows key and the C key. That will bring up the Charms bar on the right. Use the tab key to move to the settings icon and press enter. In the blue bar that opens use the tab key to navigate to the 'Change PC settings' link. You'll get an App window up. In this Window use the tab and arrow keys to navigate to the GENERAL link on the left list. Press enter. Use the arrow keys to navigate down to 'RESTART NOW'. press ENTER. I shall follow my own advice and do it now to see if I can still use the TAB, Arrows and ENTER keys to navigate to the 'fresh install' or repair or even restore to remove that third party app you've installed. Will post later.