Last week a friend gave me their comp to fix, a 2010 13" Macbook Pro. It wouldn't boot at all. It just gave the flashing questionmark folder. I tried everything I could online to get the computer to start up again, but nothing worked. Not a darn thing. I figured Command-R on boot, entering recovery mode, would allow me to fix the issue, but it didn't. The disk utility in recovery mode couldn't even see my friends' HD. Eventually, after ruling out all other options and exhausting everything I could find on Apple's website on the issue, I determined that the HD was dead and told my friend to buy a new SSD that I could install for them. Today, I put the new SSD in their computer. I created a bootable USB drive for the OSX Mountain Lion Install, and booted the computer into it. I then opened disk utility to format the new SSD. Sure enough, the new Intel SSD was there, visible and beautiful as ever. I went to reformat it to Mac OSX Extended Journaled. The first step shown was "unmounting." It hung there for maybe 45 seconds then said "Disk Erase Failed - Unable to write to the last block of the device." I tried a few more times, and it kept giving the same error. I tried just going in to re-install Mountain Lion and the disk didn't show up as a possibility to install on. At this point I became frustrated and moved on to other things. I had an external enclosure I was going to use to try to get SOME data off of my friends' old HD, so I put the HD in the enclosure and plugged it up to my Macbook. Guess what? The HD I thought was dead was VERY much alive, and working wonderfully, no issues. So now I'm stumped. The old HD didn't show up in my friends' macbook at all leading everyone to believe it had stopped working. The new SSD does show up but isn't able to be formatted. Upon installing the old HDD in an enclosure, it clearly does work. SOMETHING is wrong with my friends' macbook but I'm not sure what. Any ideas? Help? TLDR: I thought a hard drive was dead, so I replaced it with a new SSD. To install the OS, I booted Mountain Lion's install from a USB. The disk utility saw the new SSD (it never saw the old HD I thought was dead), but couldn't format the new SSD. It keeps saying "Disk erase failed - Unable to write to the last block of the device." I then put old HD in an external enclosure, plugged it up to another comp, and it worked fine. What's wrong with my macbook pro? Bad SATA cable? Something else? Any ideas of what I could try doing?