I have 4gb of ram and one day i got bored so i opened up my pc and the houses pc and i tried replacing between the rams, at the time i didn't really understand about inserting rams and different ram sizes but when i put the other pc' ram it didn't really fit and i tried pushing it down with hops it will fit, only one of the clips closed so i figured it was ok, same happened with my ram in my houses pc. So i decided to put them back in their places but when i did and i ran my pc it showed that now there are only 2gb of ram usable in my pc... Why ? (I have an Intel HD graphics system, but it only took 640mb...)