After an XP installation, you'll need to install all hardware drivers.. Did you reinstall XP using the eMachines recovery disc or recovery partition.. If so, then they should provide the basic drivers.. If not, then you'll need to install drivers such as the chipset, audio, ethernet, modem, and any other drivers needed.

In addition, since you installed the graphics card, did you also install the newest drivers for that card.. The installation CD may, or may not be the most appropriate driver for the card.

Hope this helps and let us know whether you've installed such items.

Hope this helps.