Hi,
It may not be too easy to do detailed troubleshooting through the forums, but kind of wondering if there is some other kind of hardware problem with the unit (like a bad hard drive?) rather than just an issue with using a keyboard or resetting the bios.
Anyway, assuming there is only a problem to get a keyboard working, wondering if the up and down arrow keys are working if the left and right arrow keys are not since I can still switch between the System Date and System Time in my X550CA test unit by using the up and down arrow keys in the 'Main' menu of the bios.
Also, I found if you disable the Number Lock, you can use the '4' and '6' number pad keys as left and right arrows and the '2' and '8' as up and down arrows.
Well, hope this can help, but if the unit is still under warranty and you cannot get a solution, don't forgot to check with your local ASUS support if you want to have them check the unit.
http://www.asus.com/support/callusFeel free to discuss more on the forums though and hopefully we can get some better suggestions.