New memory installed, computer won't boot

Installed additional memory in computer. Had 256 and added 512. Both DDR, 400 Mhz, 2800. New one fit great. Used good grounding when installed (have put together many before). Tried to boot and power supply kicks on and off several times and finally shuts down. Pulled the newly installed memory back out with same results. Thinking the 200 watt supply was the problem I put in a new 350 watt and had same results. Pulled remaining memory out and, of course, nothing except the beeps because of no memory but the supply did not cycle and the power light stayed on. I do have the same memory in another computer but unsure of trying it confused. I assume either, 1. the new memory was bad and somehow took out the other memory module (not sure if that is even possible - never had it happen) or, 2. somehow zapped the MoBo. Never seen bad memory make the power supply cycle on and off (like it is being overloaded I would guess). Has anyone had similar effects? Need some ideas before I fry more memory. Thanks, John