Have you checked and confirmed that the power cable is properly connected to the Hard Disk as well as the IDE / SATA cable at the Hard Disk and motherboard - might also want to try disconnecting and re-connecting the Hard Disk just in case of a loose connection.
Also, does it sound like the platters in the HDD are spinning as normal?
Could be physical damage, or corruption (of logical data) on the Hard Disk - corruption to any of the following preventing Windows 7 from booting: Master Boot Record, boot sector, Boot Configuration Data store.
In case of data corruption, you'll want to boot into the Windows 7 Recovery Environment (any Windows Vista or Windows 7 setup disc) and try the following:
1. Startup Repair
2. 'chkdsk /R' via command prompt.
2. 'Bootrec.exe' tool - Use the Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows
If you find that your USB keyboard doesn't work outside of Windows, check your BIOS options for an option along the lines of 'USB Legacy Support / Mode' and enable it, then try booting into the disc again and see if your USB keyboard works.