It's maybe gotten an error for the HDD.
You may press F10 - Setup, or F11 factory settings

Please clearing CMOS if above can resolve this issue.
1) Turn off the computer and disconnect the power cord from the power outlet.
2) Remove the access panel.
3) On the system board, locate the CLR_C M O S header.
4) Remove the jumper from pins 2 and 3.
5) Place the jumper on pins 1 or 2.
6) Replace the jumper on pins 2 and 3.
7) Replace the chassis access panel and reconnect the power cord.
8) Turn on the computer and allow it to start.

This should force your computer to boot into the backup BIOS.