Troubleshooting my router - Thomson TG 782i

Greetings.

Lately, I have been dealing with some persistent connectivity issues and am at a loss as to how to resolve them.
1. My connection speeds are significantly lower than usual.
2. Roughly twenty percent of the time, when I attempt to load a webpage, I am met with this error on every device connected to my network:
View on imgur
Afterward, I am prompted to log in, resulting in this:
View on imgur
Only after clicking through the link does the page finally load correctly.

I have attempted to run various diagnostics on my router, yet I frequently encounter
this or this.>
Occasionally, the system claims everything is functioning perfectly.

At this point, I am quite uncertain.
I have read that my current hardware is subpar—it is an older model from AT&T—but I suspect replacing it might not be as straightforward as it seems.

Any assistance would be appreciated.

Report the issue to the service provider.

ironcyclist58 said:Report the issue to the service provider.

I had intended to do that tomorrow. However, one shouldn't rely too heavily on their competence. I thought perhaps it would be simpler if I could resolve it myself somehow.

The only move you've got left is to pull the plug, give it about 30 seconds to breathe, and then flip the power back on. If that doesn't do the trick, I'm out of ideas...