The only reason it should automatically start is if you have the template scheduled.
Your PXE issue is most likely cased by a configuration issue. Check the required DHCP options are set. Unless you are using an IP helper setup the PXE rep will also need to reside on the same sub net as the machine being booted. I have also seen a bios update on the client machine resolve a PXE error. Or test a PXE boot on a different model of machine if you have one available just to make sure it isn't an issue specific to that machine.