My mac froze today and I had to force shut it down. Now I can't get it to boot, it gets to the end of the load bar and shows a blank screen with an X. I was informed to restart it while holding command R to get to disk utility and then run first aid. I have successfully made it to the disk utility screen but it is very slow and my mouse doesn't work. Using tab and the arrow keys I am able to get to the second screen but I cannot use tab to get to the first aid button. Any help?