can't update firmware on R6900 router- app won't work, and routerlogin.com won't connect

Thank you for the reply. After unplugging and disconnecting everything, then doing a factory reset on the router, then plugging it all back up and rebooting, I was able to get the internet access back thru the wifi router, and I was able to connect to the router thru my laptop and www.routerlogin.net, I then tried a manual download, both from the internet and from the saved .chk file on my laptop, and neither was successful. I am currently using version 1.0.2.8 and I was attempting to update to 1.0.2.16_10.0.42 however I get an error message that says "Firmware is invalid" when I try to download the file and update thru the internet, and when trying to manually use the downloaded file using the "Advanced, Administration, Router Update, Browse" method, the update just stops midstream and then I lose my internet connection and have to go back thru the whole process of disconnecting, resetting and rebooting everything to get the internet connection back. I am about ready to give up on the firmware update at this point. I have Comcast, a Netgear CM700 Cable Modem, and the R9600 Netgear router.