Connectivity Issue

My wife's one-year old Gateway desktop with Win XP Pro has built-in wireless
that has always worked perfectly. It connects via our home Linksys WRT54g
router. Lately, when it boots up, there's a yellow triangle on the icon in
the lower right taskbar. Clicking on that brings up the wireless network
box. It states that the Linksys connection has "little or no connectivity",
yet the speed is 54 mbps. I disconnect it from the network and then re-connect.
The dialog box for the WEP key comes up. The key is already entered. I push
OK, and then it connects to the internet.

Any idea why it suddenly began showing a connectivity problem? It always used
to connect automatically during bootup.

Thanks!
Scott