I have a dlink wireless router di 624 air plus xtreme g.

Are you operating the laptop with the wireless on and a cable too? You should probably choose one or the other and not both at the same time.

If you are only operating both computers on a wire then --

Assuming all cables are completely plugged in securely

If the problem is intermittent you may need to use your laptop in a normal fashion -- to see if any movement causes the disconnection. If there is a internottently defective cable when it is in your desktop it may fail less frequently, Meaning, it may work more consistenly because your desktop does not get moved around. (This last instance may avoid detection in this testing process)

Try swapping the laptop's cable with your desktop computer's cable at the computer end and see of the problem moves.

If it does not move you may have a problem with the ethernet port on the laptop -- end of test.

If the problem does not appear -- you may not have an issue or you may have a defective cable probably attached to the desktop now as noted above failing more infrequently so you have not observed it yet.

If it moves you may have either a bad cable or a bad router port -- continue test.

To determine which swap the cable's on the router end this time between the two attached ports (use the same ports with the opposite cable in each).

If the problem moves again it is the router port -- try switching the cable of the non-working machine to a new router port.

If the problem stays put is probably a defective cable. It will probably be easiest to replace the cable.

I hope this helps.