My laptop will no longer connect to my wireless router but my desktop still has online service.

Unless you've installed a wireless card in your old desktop you will never connect wirelessly.
Desktops don't come equiped to do wireless communications. And an "old Gateway" surely does not have those capabilities.

You have 2 options
1) Purchase and install a wireless card for your Gateway

2) Use it hard wired... Purchase an "Ethernet cable" of sufficient length and plug it into one of the open ports on the back of the router and into the only place it will fit on the back of your computer

1.Connect modem to the one separate port of the router on which you would see Internet, Wan or Lan. 2. Connect one of the Four port of the router to the laptop or desktop. 3.Insert the disk that came with the router into the laptop drive and install it. 4. Turn on the wireless services on the laptop by hitting the wireless button the laptop. 5. Now, connect to the available wireless networks.

your laptop is able to go online using WI-FI.
desktop is connected to theb router but not able to go online. Do you see the port light on the router ?
check the Ip address on the computer. Check if there is any static IP address on the computer.
Click here for more information about the router and network

One desktop and 1 laptop are working that means your router must be working.

1 desktop is not working. Is that wired to the router or wireless ?

If it is wired then check the light on the router, If your computer is connected to port 1 of the router then port 1 light should lit up. If the light is not lit up then check the connection.
If the light is lit up then check the IP address on the computer.

If it is wireless desktop then check the wireless connection.

Click Here for more info

Connect your internet connection to the port on the router
then connect your laptop and desktop to the router.
if you have a user name and password enter these in the router settings
everything should work

If you can't get online on either machine, plug your ethernet cable directly from your cable or dsl modem into your desktop. If it shows a network connection and you still can't get online, it may be a service provider problem. I am assuming that your service provider did not ship you a router, only a modem. Hooking up 2 routers on the same connection can be very tricky.

try this plug up a line to laptop to modem to check to see if you can get connected if so then make sure you are on the same network and if so then call comcast to help you setup the laptop wireless settings in sound like the settings online doesn't have the laptop enable to accept the laptop

contact your at&t service they should be able to tell you how to connect the router to your desktop and not your laptop

If its a wired connection it will automatically know that its connected to it. With the wireless you need to veiw the available networks before you can connect to the network. And if the router is already configured for internet they will automatically get the internet connection.
If you need help to make sure that the router is online. Kindly provide me with this info;

Internet service provider:
brand or model of Modem from internet service provider:
Operating system of the computers:

thanks.

Ok, you have several options. Go to a website such as bestbuy.com. Type in linksys and look of wireless access points, wireless usb adapters or a wireless desktop adapter. I would go with the third one.