Dead SB61G

Hi,
I ave a shuttle SB61G that was running fine until a few days ago - when
it stopped. The symtoms are:

When power is turned on the tellow disk activity light comes on and stays
on.
The machine does not boot - there is no output at all on the monitor - boot
no bios display - so can't get into bios setup
The monitor doesn't even come out of standby.

any ideas, motherboad, pwer supply or processor fault,

any help would be appreciated

AJ: