Grey screen upon boot, no key commands function.

If you cannot boot from the Recovery HD, then it's possible you have a failed SSD. If you have your Snow Leopard DVD, then you should try booting from it.

Reinstalling OS X Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Reinstalling OS X Without Erasing the Drive

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the Macintosh HD entry from the the left side list. Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

Also see:

Reinstall OS X Without Erasing the Drive

Choose the version you have installed now:

OS X Yosemite- Reinstall OS X

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

Note: You will need an active Internet connection. I suggest using Ethernet

if possible because it is three times faster than wireless.

Cable from what?

Are you able to do these:

Resetting your Mac's PRAM and NVRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

Yes, the internal SATA cable to the SSD could be bad. In any case at this point I don't think there is anything you can do except take it in for service.

Hi. I helped another person that had a similar problem. Here's what worked. I had them do a SMC reset as if it had a battery that could not be removed. Holding down the Command/Option/Shift keys and power button for 10 seconds. Then before they released the power button change keys to Command R. This got them to recovery. It could be done with those keys or Option/Option R or C with disk inserted. I cannot say that it will work for you. But it might. They thought there keyboard was unresponsive also. You could also try resetting the memory. I had a macbook that had a bad memory slot and it would not go to screen or give the beeps for bad memory.

Hi. If the disk you used to try a boot is the original disk that came with your macbook. You should have the apple hardware test on it also. That can be run by inserting the disk and then booting holding down option/d. The fact that you cannot boot off this disk to a install screen does sound like hardware , and not necessarily the hard drive. You may have to take it to an apple store for a free evaluation.

I Know this post is old but I thought it was helping me until I got to the disk utility but. I click first aid but none of the 4 options at the bottom including repair disk are clickable. Please help

Mac OS X: Gray screen appears during startup - Apple Support