Such messages typically appear...when the system is trying to do a network boot.
That may happen because the CMOS battery needs to be replaced...in some systems, such will make the system return to default boot options.
I would go into the BIOS and see what the first boot device is...if it's not the hard drive, try to change it and save the changes...then try to boot.
If the change doesn't hold or cannot be accomplished...I would replace the CMOS battery.
CMOS Battery Replacement - http://www.liverepair.com/encyclopedia/articles/cmosreplace.asp
, see Step 4 for Gateway details.