D-Link DI-624 router not connecting to Inspiron 8600

I just recently purchased the Inspiron 8600, so I'm new to this wireless stuff. The DI-624 is connected to my desktop through a Toshiba PCX1100U cable modem. For the first week or so, I have no problem accessing the internet from either the desktop or the notebook. The notebook connects the the internet with strong connection and signal on 2 floors up from the router. But starting last week (the 2nd week I've been using the router), the connection began to drop dramatically even feets away from the router (in the same room, 5-6 feet away). The signals on my notebook will just drop to "low", with 1-2 kbps. But sometimes, it will connect with a full 54kbps with a "very low" signal. Now, starting yesterday, my notebook won't even connect to the router when it sits right next to it. It says "Wireless network unavailable". I'm not sure if it's a problem with the router or the notebook. But the notebook can see other wireless networks in the range (neigbhor's).

 

Notebook details: Inspiron 8600, WinXP (SP2), Intel (R) PRO/Wirelss 2200BG network connection

Desktop: Windows 98

Router: D-Link DI-624 (C)