OS X partition doesn't show up after dropping iMac, Windows still works I physically dropped an iMac tonight, shattering the protective screen. The computer was sleeping when it got dropped. The drop was from a couple feet high, and booting up looked promising until I realized that I am no longer able to boot into the OS X partition, only the side-by-side bootcamp Windows partition. On holding down alt during boot, only my Windows option is displayed for system to boot into.

This seems like a strange way for things to break due to physical damage given that the Windows partition is working perfectly and there is a single physical drive.

Where can I go from here? What information can I provide to help in diagnosis?

Additional info:
All data is backed up to a local Time Capsule.
This is an old (2007?) iMac running I believe ~10.6.5, though I'm not totally sure on exact version.
The bootable partition is Windows 7.
If you are running 10.6.5, try booting from the original installation disk, then open disk utility. 

Run a "Repair Disk" both on the whole HDD to see if there is an issue with the partition table and on the boot volume that isn't working to see if there is an issue with the file system. If this disk is not repairable, you may have damaged the HDD with the drop, in which case not much can be done in terms of troubleshooting. You have a local backup, so your data is at least safe. 

Alternatively, if you have another Mac running OS X, you can attempt to mount the disk using Target Disk Mode. This will essentially treat the internal drive on the iMac as an external drive on the other machine. Then you can run the troubleshooting steps above in a similar manner.