Unable to boot into my OS X after installing Windows 8

Ok I am in major trouble here!

I wanted to install Windows 8 in my Mac.. So I used BootCamp to partion my HardDisk and allocated some 100 GB for Windows.. All was well and Windows was installed..

After logging into windows, I further portioned the C: drive, using Right Click Computer --> Manage --> Disk Management... I shrunk my C: drive from 100 GB to 60 GB and named the new partion as D: which now has 40GB.. I messed around with the system-assigned partitions(the Mac partition, a 200 MB partition and 1 other) changing the drive letters a few times

Now when I restarted the system and went to boot menu(by pressing Option button), I could only see my Windows partition.. No way to log into my OS X!

What do I do? Was my tinkering around with the system partition drive letters somehow responsible for this? If no, then what is the problem?
And how do I rectify this and log into my OS X??

PLEASE HELP!!!

Maybe you deleted the OS-X partition when creating the Windows partition, considering there was not one in the "Boot Menu".