@Buzzme 

Some browsers make it hard to connect directly.

Sometimes clearing history and cookies can allow you to gain access.

Also try a different browser or device. Been a while since I connected to my modem but as I recall, I used Safari. 
 

Also I have bypassed the router and connected my pc direct to the modem. Not ideal but works. 
 

update... I just tried it on my iPad using safari and got a secure warning message but was able to get to the sign on screen.

I tried that and it did not work. So I guess the modem is bad. I meant to say the TP LINK ROUTER MUST BE BAD

  @Buzzme 

Rare for a modem to go bad.

what lights are on when connected to your ISP?

All lights are good and it connects. I get abut 750mb wireless. UPDATE now my phone can connect to the router and 1 tv can connect. But the 2nd TV does not connect to the router. I did a network reset on the TV and still wont connect. Still cant connect to 192.168.100.1 which is the modem. I did try Chrome, Firefox, Edge Cleared cookies and even used my phone to connect to 192.168.100.1 Still cant connect to modem. I have a Asus router and it can connect to 192.168.100.1 and it works fine.

So I am going to have to get the FREE modem and router from Xfinity

  @Buzzme 

Did not think that Xfinity gateway (modem router combo) was free. My Xfinity bill went down when I started using my own modem and router but that was over 15 years ago. 
 

I use different ssids for each network as I have seen some routers try to connect 2.4 devices to the 5 ghz network. Not sure if that is your case for your tv. Sometimes the security options in the wifi network can cause connection errors for some devices. 
 

I have found the Asus router tend to be for the more advanced user but seen TP Link increasing the options in the newer routers. 
 

I almost never sign on to my modem and when I do, mostly just to see number of up and down channels it is using. It showed a list of channels and the number of errors on each channel before but no longer does so. About all you can control anymore on my Motorola SB3200 modem is the user name and password. 

  @Buzzme I have had a few Arris modems, usually there is no need to connect to them as their is nothing to configure on them.  power off the router and power off the modem.  Power modem back on and let it fully boot before turning router on.  Let router boot up and go into the admin pages of the router, it should show connected to Internet there.

Also- if it is an ISP provided modem, it may be locked out so that you can't log into it.

  @Buzzme 

Thanks for all your help everyone. I just got the new Xfinity modem and router and evrything connects fine. So the TP link router was locking out my Roku tv also Even though I did a Hard reset on the TP router I still could not connect to the Roku TV I did the wifi reset on the TV and that did not help.