It could be the PSU.
Rocketfish is a tier 5(not recommended) unit on this list:http://www.eggxpert.com/forums/thread/323050.aspx
Try removing one card and see if you run ok with just two monitors.
Then try again, using the other card and slot.
If your parts run ok individually, I would suspect the psu.
A 9800GT by itself is recommended to need only a 400w psu with 1 pcie 6 pin connector.
A second can use up to an additional 150w. 75w for the slot, and 75w for the 6 pin connector.