I would try one stick at a time in one of BOTH OF the slots to see if they are damaged or dirty. A tiny piece of lint or "micro" paper between the metal contacts could mean the difference of turning on or not. You did not say if the the memory sticks are the same speed.That causes problems! Take the stick out and REplace it in again.
Your motherboard my only recognise two of the same size or make of ram. try the 1024mb in on it's own and see if the bios allows the system to boot and recognise it. see what windows recognises, go to my computer, right click, properties and in the main window it will tell you processor speed and look to see how much ram is showing
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