First off, dont panic. The NAV system might seem as if it shot, but its designed to always boot from a NAV OS disk if one is present in the drive. Therefore, try burning the disk again.

I recomend you try Alcohol 120% (latest version, trial download available) ... and burn at the slowest speed.

http://trial.alcohol-soft.com/

Simply insert your newly burnt disk into the drive and the NAV computer should boot from it ok.

Failing all of this, try burning a fresh disk on a different computer if you have it. It could be your CD burner.