These errors occur when your machine can't "find" a boot device and looks for one on a network.
PXE-61 Media Test Failure
The first thing to check would be the BIOS settings...make sure the First Boot Device is the cd-rom drive, the Second is HDD (IDE 0), and the Third is the floppy (If present). If you end up making any changes to the settings, be sure to save them...usually by pressing F10.
A bad cd-rom can cause this problem as can loose cables and/or bent pins at the conector. Double check all your cables.
If everything appears correct and you continue to get this error, try flashing the CMOS. If you need assistance doing this, post back.