No Power with HDD connected ¿

[Mathew F]

When attempting to start my computer with the HDD connected nothing happens, however,
When I remove the power connection for the hdd the lights come on, fans start etc and the computer begins to 'boot'.

I have replaced the psu, but the same problem... Can anyone help?

I am running:
300W PSU
ECS k7s5a MotherBoard
1.3Ghz AMD Duron CPU
40G seagate barracuda HDD
64MB GeForce 2 MX Graphics Card
512MB SDRAM

[Monkeeman]

is the hdd new? and also test it in another pc to make sure its good and working order.