Strange booting problem

[JD]

Laptop: Dell Latitude E6510.

OS: F20 with all updates

Grub installed on sda.

Power up ,and after bios's internal works, I do not get the grub menu.
All I get is an empty screen with the underscore cursor blinking at 
upper left corner.

Reboot.

Press F12 to get the BIOS boot menu.

Select Internal HDD

Boots just fine.