Boot into the firmware screen and confirm the hard drive is detected.
If not then the drive is likely dead and will need to be replaced.
If it is detected you may have a corrupted boot loader (the part the computer needs to read in order to know what operating system is on the device and for the computer to know what to load to get the operating system to boot.
For the latter, the easier less technical route would be to simply re-install the operating system which for home users requires a system recovery disk or partition available on the hard drive (this is dependent on the manufacturer and model of the system) see manufacturer documentation for the available recovery process.
The more technical approach may require using a windows recovery environment or windows install disc to attempt a repair. Actions needed can vary widely and requires technical knowledge to complete.