Hi all, I have a mid-2012 13" MBP non-Retina, and its being temperamental. Apologies for the length, but here is the timeline of events: Recently, the original hard drive died in my computer - one day I tried to turn it on and started getting the flashing folder with the question mark. I tried reinstalling OS X Mountain Lion through Internet Recovery but midway through the process it quit, restarted on it's own, and left me at the flashing folder again. It had been making clicking sounds for a while so I assumed the HD was dead. So I pulled the original harddrive and installed a Samsung 850 EVO 500gb SSD. (https://www.amazon.com/gp/product/B00OBRE5UE/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1) I also upgraded my RAM to 16GB while I was in there. (https://www.amazon.com/gp/product/B008LTBJFW/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1) I booted to disk utility and formatted the new hard drive to MAC OS X Extended (Journaled). I then tried Internet Recovery again to install Mountain Lion and this time it went all the way to 100% but when it restarted after completion I was left with the flashing folder again. Yesterday, I brought it to the Apple Store near me, explained what I had done, and asked them to install an operating system on it. After a few tries they were able to get OS X El Capitan installed. When I got home I started the process of installing updates and downloading some of the apps I had lost. I saw that High Sierra was available to me, so I said why not and downloaded the installer. The installation went fine and seemed to be running smoothly, so I continued various installs. Nothing major. A couple menu bar utilities, Chome, Starcraft... Then I started the Garage Band install and went to bed. Well when I woke up this morning I was met with the flashing folder again. I restarted, holding down Option + R, and went into Disk Utility to choose my startup disk. But there were none available in the menu. I restarted again, holding down the option key this time to go into Internet Recovery, and miraculously, my startup disk was available to select. I selected it and was able to load my desk top. Then after a few minutes of use it started slowing down and eventually the screen went black and it restarted on it's own to the flashing folder. I alternated a few tries of booting into disk utility and internet recovery and was eventually able to get to my start up disk through internet recovery (holding option during boot) Right now, It appears to be working fine. But I'm scared to restart it or shut it down. Is there anything I can do while it's working right now to try and fix this? Is there a way to save a start up disk to a thumb drive to use if this happens again? Any ideas are appreciated Thank you.