I have an early 2011 17" MacBook Pro that had been working fine until just recently. (I did notice that at least since Yosemite, my restarts had taken longer than in the past. Is Yosemite a bit too much for my laptop?) A few weeks ago, I opened my laptop and the screen was messed up. There were large vertical bars, I couldn't read anything and I couldn't get the laptop to start up, even with the wacky screen. It would give me the progress bar for a long time and then it would restart itself. I saw online that this was usually due to a bad logic board and I also saw that Apple had problems with the logic boards back around the time I got my laptop so I brought it to the Apple Store and they sent if off for repair. Fortunately, they were able to produce a time machine backup of my harddrive for me before sending it off. In the past, I did make some modifications to my laptop - I added lots of RAM and changed the hard drive from 750 GB to 1.5 TB. When I got my laptop back from repair, it worked fine but it had a 750 GB drive in it. I was given no explanation as to why they didn't leave my 1.5 TB drive in the machine. The clerk who gave me my laptop simply suggested they must have found something wrong with the hard drive. So great, I now had a backup that was too big for the 750 GB drive. So I needed a new hard drive, since I didn't want to take a chance with the 1.5 drive. Went to Best Buy and bought a Seagate 2 TB drive (I hate Seagate, but it was all I could find in short notice). I should mention that I had used the laptop with the 750 hard drive for a little bit and had no issues with it. I put in the 2 TB drive and I restored from the time machine backup. But all was not quite right. It felt like the machine was not starting up right - it was really slow. And then I was hearing some noises coming from the hard drive area - a periodic grinding chirp and a single long tone. Once the laptop was up and running, it worked fine except that I heard these noises. So I sent it back to the Apple Store and fortunately the techie at the store was able to see some of the odd behavior, though he did not get to hear the noises. He noticed that sometimes the laptop saw the hard drive and sometimes it didn't. He opened up the machine and noticed some bracket on the logic board was broken and that my status light wasn't working. So he figured they broke something with the last repair. So we sent if off again (he put the 750 GB back in the laptop first) and I got it back, again with no idea as to what they did to the machine. There was some suggestion on my receipt that they replaced the logic board, but it's not clear. I used the laptop and it was working fine, but again I needed the larger drive. So I put the 2 TB drive back in the laptop and the noises returned. I called Seagate and the tech suggested I do a clean install of Yosemite, since maybe my time machine backup was faulty. So I saved all my data onto an external hard drive and created a flash drive installation disk for Yosemite and did the clean install. Didn't help. Noises still. Grr. And now this morning when I woke up my laptop, I saw a flashing folder on screen, which I believe means the OS could not find the startup disk, my hard drive. The only thing I could do was hit the power button, turning it off. I waited and then turned it back on and as I kinda expected, I was in and it was working as before, still with a slow startup and the periodic noises. Can anyone suggest what could be happening? Is it just a faulty hard drive? Could a faulty hard drive cause this behavior of sometimes working and sometimes not being seen by the OS? Or is there something wrong with my laptop? Is there a problem with using this 2 TB drive with my laptop? (http://www.bestbuy.com/site/seagate...ulti/7523041.p?id=1219277910533&skuId=7523041) The hard drive is 6 Gb/s transfer rate and I think I remember reading something about a firmware upgrade for my machine in the past that brought the transfer rate from 3 Gb/s to 6 Gb/s. (http://blog.macsales.com/11895-2011-macbook-pro-sata-problems-resolved) Might I be experiencing some sort of incompatibility? After I had restarted my laptop, it gave me an error report to send to Apple. I copied it. Let me know if it's worth posting it here. FYI, since it was past Best Buy's 15 day return policy, I am working with Seagate to get a replacement hard drive which will hopefully arrive by the end of the week. Maybe all this is is a bad hard drive, but I'm not so sure. Thanks!