Computer loses connection to router

Hi guys. I have a Dell Dimension C521, and I'm using it as a server. I don't want to have a mouse, keyboard, or monitor connected to it. I administer it using remote desktop (it's running XP pro SP2). However, if I don't leave the mouse and keyboard connected, then computer disconnects from the router after a few hours. I have the computer set to never turn off anything (besides the screen), and the wireless adapter is still flashing even when it's disconnected from the router. I don't have a good spot to put it near to the router (thus I'd be able to use Ethernet), so I have to use wireless. I don't have a spare mouse and keyboard to leave always plugged in either. Any ideas as to why the server would suddenly disconnect itself from the router, but not turn off the wireless adapter, hard drives, or anything else? And yes, I do have all drivers for the wireless adapter installed.