If I'm reading that right, your saying you've removed the IHS, reseated the water block but the system powers off after a couple of seconds?

If so mine did that the first time I mounted the block after removing the IHS, it was a bad contact between block and core...cpu was overheating in a couple of secs and the thermal diode in the chip cuts the power before any damage happens.

Have you tried remounting your water block?

Apologies if I have read your post incorrectly.