PXE it an option in your Boot order in the BIOS.
Defined by Webopedia...
Short for Pre-Boot Execution Environment. Pronounced pixie, PXE is one of the components of Intel's WfM specification. It allows a workstation to boot from a server on a network prior to booting the operating system on the local hard drive. A PXE-enabled workstation connects its NIC to the LAN via a jumper, which keeps the workstation connected to the network even when the power is off. Because a network administrator does not have to physically visit the specific workstation and manually boot it, operating systems and other software, such as diagnostic programs, can be loaded onto the device from a server over the network.
PXE is a mandatory element of the WfM specification. To be considered compliant, the PXE must be supported by the computer's BIOS and its NIC. PXE