shuttle wont boot

My sn85g4v2 won’t boot into Windows. I get the bios splash screen but cant access the bios because my keyboard wont respond. The machine hangs at a black Windows message screen which I cant respond to as the keyboard isn’t responding.
Both keyboard and mouse are usb. If I disconnect the mouse and reconnect it, the laser light shines briefly then disappears. If I try the same with the keyboard, nothing lights up.
Can anyone suggest any possibilities or tests I could make?
The machine has a Santa Cruz sound card, 9500 pro graphics and an Athlon 3gig chip.
Thanks.

Have now had time to have a good fiddle with my machine - had no forum responses, so it was the usual battery of tests.

I started by resetting the cmos - no difference.

I then removed the mobo battery to test it - and guess what -the machine fired up! Yes, thats right, it failed with the battery (which incidentally, was charged) but worked again with it removed.

How can this be - surely the bios needs the battery to help with mobo settings?

Any ideas, explanations anybody?