Hi,
Backup your data to external media and be sure that you have created the external HP recovery media.
Try a Windows 8 repair process.
It's possible that the Windows 8 boot loader is pointing to the wrong location along with other numerous possibilities.
You may have to use the HP recovery media to reload the system. Another possibility is to use a third party product like Paragon's Hard Disk Manager Suite 14 which supports Windows 8 and Windows 8.1
In the worst case seniaro, you may have to remove CMOS battery for a few minutes. After reinserting the CMOS battery then use the HP recovery media.