TL;DR: SATA cables in my MacBook keep failing; Something in there has to be messing it up, but what? I have a 13" MacBook Pro from 2009 and I've never had any real problems with it until this year. My MacBook wasn't booting from its internal SSD, so I put the SSD in an external drive enclosure and it booted without any problems. I paid an Apple store to replace the SATA cable and everything was fine. About a month later, I started having the same problem. I took my Mac back to the Apple store and because the replacement SATA cable was covered by a 2 month warranty, they replaced it again for free. Now it's having the same problem, yet again. The battery in my MacBook has seen better days. For a few months, the battery status read "Service battery" and now it reads "Replace soon". In the Help screen, it said sticking with an old battery wouldn't do any harm, but is that correct? Could the battery be outputting higher voltage or something? My MacBook didn't originally come with an SSD; it had a 250GB hard drive. I upgraded it to a 512GB Crucial M4 in 2012. I'm sure that isn't causing the problem because it was fine for the first 18 months. My MacBook also has 8GB Crucial RAM, upgraded from the 4GB it came with. I'm sure that's also fine, but I'm mentioning it because it wasn't included with my Mac. My MacBook has a couple of dents in the bottom case from the amount of times it's been dropped. I assume it's nothing more than cosmetic damage, but it is metal; Could it be shorting the SATA controller? Excuse the long post; I just thought I'd mention all the possibilities I could think of. Thanks in advance for any replies.