I just bought a stick of 512 pc2100 RAM but when I put it in my computer, it beeps as if there isn't any ram in it at all and nothing shows up on the monitor. I assumed that it couldnt go together with my 256 so i put it in by itself. Same problem occured. I tried both slots, still wont work. here r the specs: 512mb, ddr, 266, cl2, ecc. I ran everest home edition and it said my cpu doesnt have ecc and the my 256 ram runs at 166 mhz (odd). Is the 512 mb ram not compatible with my mobo or something. I mean heard people say that pc2100 is compatible with mobos with pc2700 ram. Or could it just be broken? Is there any way I can get it to work?

that ram is not compatible with the board.
check the ram tho
www.crucial.com
run free ram test there

is it because its ecc?

You can't mix ECC and nonECC memory and most MBoards for PCs don't use ECC memory.