Seeing as it was shut off ,you can't use the option of re-installing the old bios

If you had a hardware fault then updating the bios when it's unstable isn't a good idea

,or did you mean you'd discovered a software problem with your old bios version?
Anyway ,AFAIK your options are limited to :-
1.Hot swap the bios chip from another identical working mbrd to enable you to reprogram your bios chip.Assuming you can find a willing particepant ,& you have the right bios extraction tool.
2.Send your mbrd off to Asus to be re-programmed ,BUT I don't know how much that would cost & whether it would be worth it.
3.Buy a replacement 2nd hand mbrd
4.Take the opportunity to do a mass upgrade

(& flog off the working old bits)
This of course is assuming their isn't some other fault with your PC.
When you said
and the computer wouldn't boot ,what exactly did you mean? ,because if you could get into the bios then it could boot to some degree naturally.