The BIOS you can configure the boot order priority of devices but to locate the OS, partition etc that is the job of the MBR.

Back to the OP, you DON'T need install media, if you load the "Advanced Boot Options" I.E pressing F8 on startup you will see one of the options there is "Repair your computer" which is your best bet (Although it may be worth trying "Last good known configuration" first.

Martin