Weird disk issue

I'm having a strange problem with my primary hard disk. It won't spin up when the computer has gone past POST. This means if I just flip the box on, it won't boot, however if I hold the reset switch in till I hear the disk spin up fully then it'll boot fine.
Anyone have any idea what could cause this?

Pertinent info:
Disk: Maxtor Atlas 15K II 36GB u320
Controller: Adaptec 19160

The disk has been installed in this machine for months without issues prior to this, and I've not changed anything in the past few dayas in the setup of the machine as a whole.

whats the delay motor start jumper setting?

Whatever it's always been. :p

Delay spin and staggered spin are off.

I just turned delay spin and staggered spin on, comp booted straight up.

EDIT: Found a better manual on maxtor's site, know now which way round the jumpers are. :p

If you've got spare time, and are worried as to why the issue just started to present itself (assuming it just stopped working all of a sudden)

Try a different PSU!
Would be intresting to know why it needed it all of a sudden.

I don't have another PSU that can actually power my main box (it needs 450W+ being an sli machine). All my spares are crappy 300W jobbies.