MacBook Pro boot issue I put my MacBook Pro to sleep at night and the next morning when I try to boot it .. I get a question mark icon on a blinking folder... I long press the power to shut it down.  

After some time when I try to boot again I no longer see the same error icon, instead i see the Apple icon followed by the user accounts (one main account and the other for the guest user). After keying in the password the OS seems to load as I can see on the progress bar. But then it stops and there is a blank screen with a prohibited sign on it.

This is what I have tried so far. 

I have gone to the Disk Utility window and I have tried to verify the disk and the results tell me that it is corrupted and needs to be repaired. But the repair disk button is disabled. Also i am able to boot using the guest user account just fine. Can someone please help me out?
You need to boot into Recovery Mode to be able to run a disk repair in Disk Utility.

Press and hold ⌘+R while booting, once you see the Apple logo you can let go.

Because your disk is encrypted, try mounting it first by opening Startup Disk, and choosing your disk as the start up disk. This should mount the drive.
Then quit Startup Disk and open Disk Utility as below.

Then you should see a menu bar with a Utilities option in it, choose Disk Utility from here and run the disk repair.

Unfortunately, disk failure is a possibility, but it could also be corruption from the system going to sleep while in the middle of doing something.
If you do manage to get back into your disk, I would recommend making a backup as soon as possible, as well keeping a regular backup in general.