Wireless Router - having problems with only one connected machine/device

"Looking on dlink.com (click Support Resources then Firmware), I can see that your router model has a firmware update to version 1.9 dating from 9/10/2008.

If you don't have this version, you might consider first updating the firmware before examining further the problem, since this might be a firemware bug that was already fixed in the newer version. This will also reinitialize the router to a known good state."