Hmm.. is it dieing?

[Private_Ops]

I have a SeaSonic 330w PSU.

Everytime I turn the computer on it shuts off.

I've concluded that its during HD spin up because with it unplugged the system POSTs just like normal (just no hard drive).

I've also noticed when the HD spins up I can hear a rather audible "hissing" noise coming from the PSU.

Any idea what could be going on?