There a lot of problems with the Comcast routers!
Try a reset to factory defaults, press and hold the reset button on the back for 5 seconds. Then login in using the default userid and password ("admin" and "password", respectively) and reconfigure your wireless network. Any better? If not, I'd consider replacing the router with a better, more modern model, this is a very good one; http://www.tp-link.us/products/details/?categoryid=238&model=TL-WR1043ND
Longshot, but try changing your brightness setting & then try connecting.
Look at iOS Troubleshooting Wi-Fi networks and connections http://support.apple.com/kb/TS1398
iPad: Issues connecting to Wi-Fi networks http://support.apple.com/kb/ts3304
iOS: Recommended settings for Wi-Fi routers and access points http://support.apple.com/kb/HT4199
Additional things to try.
Try this first. Turn Off your iPad. Then turn Off (disconnect power cord) the wireless router & then back On. Now boot your iPad. Hopefully it will see the WiFi.
Go to Settings>Wi-Fi and turn Off. Then while at Settings>Wi-Fi, turn back On and chose a Network.
Change the channel on your wireless router (Auto is best). Instructions at http://macintoshhowto.com/advanced/how-to-get-a-good-range-on-your-wireless-netw ork.html
Another thing to try - Go into your router security settings and change from WEP to WPA with AES.
How to Quickly Fix iPad 3 Wi-Fi Reception Problems
If none of the above suggestions work, look at this link.
iPad Wi-Fi Problems: Comprehensive List of Fixes
Fix iPad Wifi Connection and Signal Issues http://www.youtube.com/watch?v=uwWtIG5jUxE
Fix Slow WiFi Issue https://discussions.apple.com/thread/2398063?start=60&tstart=0
Note - When troubleshooting wifi connection problems, don't hold your iPad by hand. There have been a few reports that holding the iPad by hand, seems to attenuate the wifi signal.
If any of the above solutions work, please post back what solved your problem. It will help others with the same problem.
I got an Arris TG 862G gateway from Comcast (BUT THIS FIX MAY WORK WITH OTHER ROUTERS/GATEWAYS).
Had trouble accessing the router at first but finally got into it by putting http//10.0.0.1 into browser address field. Default name is: "admin", PW is "password". (Access info is on the net for all routers/gateways)
Anyway, I had been using the default wireless password, which was long and is case sensitive. Was okay with that until I tried my iPhone 5. Got "Cannot connect to network" or something like that. iPhone 4s, iPad, and Mac Pro worked fine. Note: This is different than having the wrong password, in which case it says "Wrong password" or something like that. I had seen this problem on one other gateway (from Sonic) with my iPhone 5, but I just ignored it because it wasn't anywhere I needed to be often.
The upshot is I decided to change both the network name and wireless password in the gateway settings for convenience reasons (I used the "Wizard), BUT THIS FIXED THE iPhone 5 PROBLEM! Just changing the password is what did it, I believe (My next step was to change the security type, but that turned out to be uneccesary). I had seen this mentioned somewhere before but it made no sense. What does the iPhone care what the password is? So try this first if you are having a problem. I used a simple password. Could it be the iPhone 5 needs shorter passwords?
Note: Network name and wireless password are different than gateway/router access name & password. The access passwords are to get in and change things. The network name is what shows up on your device, and the network PW is how you access the network (with your computer or iPhone). I'm sure this is obvious to most of you but many folks seem confused by it. You can change both once you are in the router settings. What I am talking about is the wireless password.