Having the same issue. Yesterday out of the blue my iPad isn't connected to my home network...I try to connect and told password incorrect even though it is. Today same issue with my iPhone (was connected fine yesterday). I'm sure it's just a matter of time before my laptop is bounced off...I need internet to work from home....and it's a Sunday so comcast store not open. Grrrrrr
If this is a Comcast supplied gateway device, see if you can view what your password currently is online;
I'd reset the device back to factory defaults. Depress the little button in the hole on the back with a paper clip or similar device for about 30 seconds. You'll lose any custom settings.