Computer wont boot after installing new RAM.

Ok im pretty nubish but ill try to describe my problem. I had 256mb of ram. The kind with 2 notches in it. I wanted to upgrade my RAM so i talked to the guy that built my computer. I figure he knows what kind to get me because he put the thing togehter. He got me two 512 cards with one notch (ddr i think). My MOBO has 2 black slots for the 2 notch cards and 2 red ones for the 1 notch cards. I pull my old card, snap the other two in securely and start it up. Everythign lights up and spins but "no signal" tp the montior. I Pull one out and try, no luck. I replace it with the other, still no luck. i stick the old 256 card in and everything is fine. here is some specs.

Intel P4 2.00ghz
Bus-ISA AGP PCI USB i2c/SMbus
System BIOS- America Megatrends Inc. 07.00t
Mainboard-ECS M922
Total Mem-256MB SDRAM
Chipset Model- VIA VT8753 Apollo P4X266
NVIDIA Ge Force4 MX 440

I am pretty sure i didnt damage the cards, so what could be the problem?

Thanks in advance,

matt