Help! Crucial memory upgrade not working

Hi, I'm hoping someone can give me some easy advice that will solve my problem.

I am trying to help my 15"powerbook 1.67 last as long as possible so I ordered a memory upgrade from Crucial going up from two 512mb to two 1Gb to max out my RAM. I used the Crucial software which tells you what your system is and what spicific Ram you need so I am confident that I have the right type, however when I install it, my laptop wont start, I here the startup sound and then a long beep, no screen at all, and the power light blinks every few seconds.

When I reinstall my old Ram then all is well so I am fairly confident that I am installing it correctly.

Crucial support is not available until monday but I would love to get it sorted as soon as poss.

Any help, advice or instructions would be really appreciated.

Thanks