A superficial but simple solution may be to go into Control Panel
(right click an empty spot in Metro Start screen and choose ALL APPS
in the bar that appears at the bottom. Control Panel
should be near the right side of all the icons)
(You can also get to Control Panel
by going into the desktop, opening Windows Explorer
and choosing DESKTOP
in the left pane and Control Panel
will be an icon in the right pane)
In Control Panel chooseSYSTEM | ADVANCED SYSTEM SETTINGS
choose the ADVANCED
tab and click the SETTINGS
button under STARTUP and RECOVERY
Choose Windows 8
as the DEFAULT OPERATING SYSTEM
and clear the check box next to TIME TO DISPLAY LIST OF OPERATING SYSTEMS
(or set it to a short amount of time in case you wish to add more OS in the future).
Let us know if you try this and how it works.
A more in depth solution would be to edit the BCD unless this is an issue with a GRUB loader or something similar though it does not sound like that
Editing the BCD may be more trouble than it is worth.