I have a Dell OptiPlex 380 with Windows XP SP3 installed. I have a 2GB RAM module installed that is recognized as such in BIOS. However, once Windows is booted only 512MB is usable. I have tried replacing the module, placing 2x2GB modules in the available slots, and replacing the mobo but nothing has worked. Windows does recognize that a 2GB stick is installed, but only 512MB is usable. Anyone have any ideas about what may be causing this?