|It's extremely unlikely you actually need 4gb of ram. |
The 4gb virtual memory address limit for 32 bit operating systems.
An example of 3gb working better than 4gb in a 32 bit operating system.
See Response 6:
The ram must be compatible with using it in your mboard. In the worst cases of incompatibility your mboard WILL NOT BOOT all the way with it installed, and the mboard may not even beep.
OR - the ram may not be recognized at all, or it's full size is not recognized, or installing it causes ram errors to be produced.
See response 5 in this for some info about ram compatibilty, and some places where you can find out what will work in your mboard for sure:
Correction to that:
If you have brand name ram, it is usually easy to look up whether it's ID string (part number) is in a list of compatible modules found by using your mboard or brand name system model number.
If the ram is generic, that may be difficult or impossible.
If you mix ram modules that use different voltages, the bios will set the voltage for all the modules to the lowest voltage, and the ones that use a higher voltage will not work 100% correctly.