Your PC is trying to boot and either it can't find the hard drive to boot to (so it's trying the other options in your boot order), or your boot order is wrong and network (PXE) is listed before your hard drive.
It is trying to PXE boot over the network. It's telling you that you don't have a network connection to attempt a PXE boot. If this computer was working before and just starting showing these problems then it's most likely that you have a bad hard drive.