Macbook Pro Won't Boot - Folder with Question Mark - Spinning Wheel Solution

I am not writing a question, but posting a solution here. I have a Mid-2012 13" Macbook Pro and had some major issues with it. It started when I would get the spinning beachball constantly and it would be abnormally slow for the computer to process anything I was doing. Sometimes up to a minute for it to register that I clicked a link or several minutes for it to open an application. I tried all the fixes I could. Tested in a new user, reset PRAM, cleaned out my hard drive, and even clean installed my operating system(which took upwards of 6 or 7 hours to install). After all of this, and lots of research on the discussion boards, I came to the conclusion it was a hardware issue. I decided to try replacing the hard drive first. It was the quickest, easiest, and cheapest place to start. I bought a hard drive off of Amazon that was larger and faster than my previous hard drive. I saw this as a great opportunity to upgrade. It wasn't expensive, around $70. I installed it in the computer and installed the operating system OS X Yosemite. It seemed to work. I no longer had the spinning wheel all of the time and my computer seemed to be back to normal......Until I went to start it up, wake it up from sleep, shut it down, or restart it. Most of the time I would get the "do not enter" or prohibitory sign when starting it up. Sometimes I would get the folder with the question mark, and then after resetting the PRAM several times and resetting the SMC, eventually it would start up and load the operating system. I searched and searched for answers through discussion groups and even visited some Apple stores, official and 3rd party, and kept finding that the logic board could be the issue. This didn't make sense to me because when the computer would actually start, it would run fine until it went to sleep or I had to restart it. As long as I kept it awake at all times, it worked. This was terribly inconvenient! Finally, deep in a discussion board that I can't seem to find again(or I would write a heartfelt thank you to the person who posted it) I found a solution!!! That person stated that the cables that connect the hard drive to the logic board in Macbook Pros are notorious for not being able to handle a higher performance hard drive. I bought a new cable, making sure it was made for my computer specifically, and since I was out of warranty on mine, making sure it was not the same one that originally came installed in my computer, and installed it. Viola! It worked! No more startup issues! No more issues with waking up from sleep or shutting down! I hope this helps someone else out there who is having the same problems I was. It took me months of research and reading to finally get the answer I needed.

So, abnormal slow performance? Spinning wheel constantly? You have tried all the software troubleshooting steps? Probably the hard drive.

Did you upgrade the hard drive (HDD)? Are you getting the prohibitory sign or folder with a question mark? Tried all the software troubleshooting steps? Try a new hard drive connecting cable. They are very inexpensive and easy to install yourself.

Good Luck!!