No boot or POST on Biostar M7VKB and M7VKD boards

My company has a couple computers based on Biostar mainboards that have
recently stopped functioning entirely. One is a M7VKB, the other a M7VKD -
if it was only one machine, I'd think it was some random failure, but the
same behavior from two separate (and similar) boards seems suspicious.

When powered on, the main power light, HDD activity light, and CD-Rom light
all come on steady and stay on, CPU and chipset fans spin up, and that's
it - no POST, no video, nothing. The hard drives do not appear to actually
spin up.

I was going to try to flash the BIOS, but I don't think the machines ever
get far enough to try the floppy drive. Before I fire off an e-mail to
Biostar, does anybody have any ideas what might cause this?

Thanks in advance for any and all help.