"No signal" message on monitor when trying to boot PC
I am currently building around a dozen pcs and have come across a problem. When I start the computer it powers up and a message comes up on the monitor saying "No signal" and stays like this(happens before reach the bios option). Everything else seems to be working, motherboard has power, video card has power. I tried swapping the video card with one that I know definately works and still I get the same problem.
Of the 8 I have built so far I am having this problem with 2 and the rest are working fine. They have all been tested on the same monitor & cable. When I boot the ones that work I get the same "no signal" message but this only last for about a second, then goes as normal through the system check.
The systems specs are:
MIS MS-6330 Lite m/board
Hercules Prophet 64mb 4500
Mitsubishi DV17NF monitor
128 MB ram
I would really appreciate any thoughts on this frustrating problem. Thanks...