Beep codes? Take out the memory and reseat it. If you did not get the memory all the way in the BIOS will not boot. If you are getting a beep code from the motherboard (or if it is a newer one with a boot LED) you need to look up what exactly it is telling you. If you reseat the memory and it still does not boot, try pulling out and reseating the expansion cards (though at BIOS boot time it only cares about finding a video card, and you said that was integrated). If that does not work, then there is the chance the memory you added is bad. This can be confirmed by removing the new 256MB module and seeing if it will boot at that point. You might also want to check the motherboard manual to make sure it can handle 256MB memory modules.