While you are waiting for the foam strip for your 3400...

Dan Cochran claims to have found an (admittedly temporary) solution to the RAM seating problem in PowerBook 3400s - one that you can try while you wait for Apple to ship you an foam strip (as described previously). The solution is to press the Control-Option-Command-Space keys down all at once (holding them down a bit firmly). To find out why this may work, click here.