I'm not sure this would help but it might. Have you tried entering the MAC address of your laptop into the routers configuration utility? I have a Linksys WRT54G version 5 and that's what I've done so that only my laptop and my son's computer are the only computers to access the router.
What you need to do is to go into your routers config utility by opening a browser window and inserting your routers IP address, which should be 192.168.1.1 unless you've changed it to something else. After that enter the username and password. After you're in, then click on 'Access Restrictions' then click on 'Edit List of PC's' and enter the laptops MAC address.
To get the MAC address, all you have to do is open a DOS emulation windows. If you don't know where that is, just type in cmd in the search field and then you'll see it come up. After you open up the DOS window, type in getmac and the first address on the left is your MAC address on your laptop. BTW, you want to be on your laptop when you do this....hehe.
Ok, now that you've got your MAC address, go back to your desktop PC and enter it in the window that popped up when you clicked on 'Edit List of PC's'. Enter the MAC address of your laptop, click Save Changes and then make sure you check Enable by Status and also make sure that the Allow is checked under the 'PCs' listing. Finally, check, Save Settings and hopefully you'll be able to keep that connection to your router.
Let me if this works or not.