Ashley,
When you reboot the computer and it very briefly shows how much RAM you have MBs in the scrolling text, does it show that you have the full 2048 MB?
If not, then reset the BIOS back to default settings, then restart again to see if shows at boot afterwards.
If still not, then you may need to flash the BIOS with a new version (if available) for your specific motherboard/computer model number.