I have now tried opening the iMac and removing the cables to the SSD, it still gets stuck on the white screen. I tried again, removing the cables to the HDD as well and the same thing occurs.
No idea what to do from here.
I've done quite a bit of troubleshooting and this problem sounds like mine except that I have an iMac, not a MacBook.
While using Windows 7 (via Bootcamp) I shutdown my 27 inch 2011 iMac. After it was shutdown I pressed the power button to turn it back on, it proceeded to play the startup sound and then froze on a white screen. There is no cursor or anything else on the screen.
I tried unplugging all cables, including the power, reconnecting only the power and attempting to turn it back on with the same result.
It does not respond to any key combinations. Holding Alt while it boots does not bring up the disk selector. Holding T does not put it into Target Disk mode. Holding Cmd-Opt-R-P does not have any affect. Holding Shift does not put it into safe mode. Holding Cmd-V does not bring up verbose boot.
I made a copy of the OS X Recovery Disk onto a USB but am unable to use it as the Mac won't boot from it (and won't bring up disk selector to select it).
It was working fine minutes before I shut it down and then suddenly refuses to boot and I am at a loss as to what to do. Sadly, there are no Apple Stores or Genius Bars in my country, so feel free to point to any and all self-help resources I might use.
Best Answer
Here is what you know from your excellent details:
Why the keyboard isn't working isn't yet clear. I would disconnect everything including the power and then remove both RAM sticks - noting which was on the top and which was on the bottom.
Next, plug the Mac in and power it up with nothing connected. You should get three beeps indicating the POST (power on self test) detected no RAM. If you have severe hardware problems, it won't know the RAM is missing and you'll know you need to get inside to fix it.
Assuming this works, power it off after waiting to see if it boots in 5 minutes time (really wait that long for the Apple logo to show up). While you are waiting listen carefully for rhythmic noised from the hard drive. It shouldn't keep seeking past the first 45 seconds and if so - you will know the controller or the drive is faulty. It should spin quietly after a few minutes or be reading the drive if it's corrupt and the hardware / OS is trying to fix things.
Next - power it off by the button and put the "top" piece of RAM in the "bottom" slot and repeat. Lastly - if you get to the white screen at this point, try another keyboard (command-s or shift held down are the best options here for troubleshooting) to see if you can isolate the failure further.
I tried to make some assumptions about what is wrong and you can edit the question or ask another with the step that fails referring to this question if you want to isolate things further before attempting a repair.