I’m guessing this happened after migrating to a new hard drive.

Try this:

If you don’t have the windows 10 install cd:

1. Download the Windows 10 installation files.
2. Create a Windows 10 bootable media.
3. Boot your computer with the bootable media.
4. Click the Repair your computer
5. Click Troubleshoot. Then click Advanced Options. Then click Command Prompt
6. Type the following commands to fix the mbr:

• Bootrec /fixMbr   (This will  attempt to fix the master boot record)
• Bootrec /fixBoot
• Bootrec /ScanOS (This will scan to see if there’s a windows  OS on any of the partitions)
• Bootrec /RebuildBcd   (Windows boot configuration data (BCD) Rebuild)  (This will let you select the OS partition )

Some more info:
/fixmbr replaces the information and small executable that reads the partition table to find where the OS may be located. So this exists on any drive that has been formatted and effectively exists to read the next little bit on the hard drive that tells where the/an OS is supposed to be located. In essence, this is not necessarily a Windows-specific item.
/fixboot replaces the next part – the entry in the partition table that points to where the actual loadable executable is located for the OS. So this is fixing the next link in the chain of the boot process. This command does create a windows-specific result in that it reminds the hard drive where to find Windows in particular.