Help with replacing mobo/psu. (E-machines)

That is a pretty general question as you didnt give much details to whether or not you are replacing the Motherboard with the exact same one or an upgraded one. As long as you are getting one that is compatible with the processor that was in it to begin with, then you should be able to use the same CPU heatsink/fan (be sure to use thermal paste). Even though the fan should still work, I like to replace heatsink/fans when I replace motherboards as they are not expensive and you may get a little better cooling (especially if the old one was stock). The RAM should still be fine as long as it is compatible with the new board (i.e. if the RAM is DDR and the new board uses DDR). The only way to tell if the RAM is still good is to try it in another system or try it in the new board. Hope I helped.