Looks like it's configured to network boot, which is a good way to do things in these kinds of systems. My guess would be that the network boot server is down or there's a networking issue (someone unplugged it lol)
I'm picturing an ancient Gateway 2000 tower with a finally-failed WD Caviar 20.4GB drive. 19 year old IT tech looking at the whole thing trying to figure out how much modernization he can get away with in the wake...
Have to admit I didn't open the pic big enough to really investigate. I always love these errors displayed on public-facing displays, a sort of accidental dropping the facade of seamless operation.