best steps to diag a boot problem is to start with the BIOS,
Check the drive is showing up to begin with, if yes, then get yourself a windows disk to get you to the install section
Hold shift and F10 to bring up the command prompt and attempt a checkdisk to repair any corrupted data using the following command.
chkdsk C: /r
the scan could take a few mins up to perhaps an hour or more depending on the state of the drive, but you may see it fix all sorts of problems.
I find that fixes a lot of peoples boot issues.
If your bios isnt showing the hard drive, you may need to seek some expert advice to get the drive tested in another system.
Best of luck however. hope the above helps