so my computer has been functioning great for years, but I came home the other day, and it had shutdown. When I turned it on it just kept restarting over and over... It gets to the gray screen after the apple logo and then repeats. I've spent the last few days working on it and got it up and running using recovery mode and a few other things. Reinstalled the OS, and was able to back up. It was still running slower than normal, but seemed to be ok. I restarted a few times to see if it would start back up ok and it did. However I got home yesterday and it had shut itself off again and is now stuck rebooting again Any ideas what could be wrong? Do you think the hard drive is going? Something else?