Could be any number of things. When you say you have a 3.2GHz AMD, do you mean an Athlon 3200+? If so, be aware that this cpu does not actually clock at 3.2GHz, it runs at about 2.2GHz instead.
Is the mobo dual channel? If it is & you're trying to use the dual channel mode, it will not work if the 2 DDR modules are different sizes.
Do you get any beeps when you power the system up?