Then' I'd say it's a power supply issue. If you have a spare PSu or can borrow one, connect it and test.
Or let me ask again, If connected to the motherboard and pressing the power switch, do some fans spin, but the pump?
If no fan spins, then try disconnecting the power and reset switches and start the board by shorting the 2 power pins.
If nothing, then it might be a motherboard issue.