Stopped working with internet modem supplied by AT&T and the AT&T service tech. said to contact DYNEX to soulve the problem of connectivity

This is a product that will support WiFI. Here is a description of it:
Touchstone; TG862A/NA Wireless eMTA;
DOCSIS 3.0, 802.11n, 2.4GHz, 4 Gigabit
Ethernet, 115-240VAC, 50/60 Hz North American Power cord,
If tech from service company could not activate service, I assume he feels something is wrong with the modem itself. Are you connecting over frequency 802.11n to the modem, perhaps it is not seeing the wireless frequency?

clarification in regard to the instructions that came with the installation package, I learned that you first have to connect the modem/wireless router to the PC with an Ethernet cable, before you can actually go wireless! Once I relocated the computer to where the router was, the tech service person got all the necessary info from me to activate the wireless feature, and I was then able to haul everything back to where I'd had it in the first place. I also had to get a USB wireless adaptor, with the tech service for its manufacturer helping me to get it set up. (Obviously, I'm pretty helpless on my own. )

The setup has worked pretty well since then, except that every once in a while, like you, I have to "repair" the wireless connection. But on two occasions I was not able to connect to the Internet, getting the message: "Internet Service Provider Not Found." At those times, the Internet indicator light on the router was red instead of green. After I disconnected the power supply to the modem and then reconnected it, it reset itself, the Internet indicator turned green again, and I had no trouble getting back on the Internet.

If you haven't already done so, you might check the Internet indicator light, and if it's not green, try resetting it. And if none of the suggestions offered by other people on this site solve the problem, I'd contact your ISP's tech service and/or the wireless adaptor company's tech service, to make sure everything is properly configured. I have found most of the tech service people I've dealt with to be patient and helpful.

First off, verify that you can connect to your cable modem directly. After that, hook up your Dynex wireless router and reboot your cable modem. After this, directly connect your computer to the Dynex router (using a cable). If you cannot get an Internet connection, then there is some issue with your Dynex router configuration. It's possible that there might be an IP address conflict with the cable modem. It would be best to contact support for configuring the Dynex.

If you can connect to the Internet with your computer connected directly to the Dynex router, then there must be some router configuration problem affecting your ability to connect wirelessly. You'll have to check the configuration--might be a good idea to completely reset the router and start over. If that doesn't help, you should contact Dynex customer support, as each router has its own configuration specifics. Good luck.

1) With direct connect with modem, check the IP address and default gateway.
(I came across such a modem, it gave default gateway as 192.168.1.254)
I also had the doubt of configuring as a dynamic connection
But it won't work!
Contact your ISP to completely bridge the modem and configure the dsl modem as PPPoE connection with correct username and password.
Finally connect the modem to router and do a complete network power cycle, i.e.: Unplug power from router 1st, then power from modem, unplug the telephone line and now do the exact reverse process... Plug back the tel. cable, then power to modem... now WAIT for lights on modem to come back, then plug in the power to router. This will surely work.

Unplug the router for ten seconds and plug it back in, it needs to reset. Some routers have a reset button. I often wait longer than ten seconds, I find a beer is usually the right amount of time. Sometimes the modem needs a reset also; unplug everything, then plug back in sequence, with the modem first, the wait, then the router, wait, then turn on your computer. That system works for any brand modem and router.

First, power down all equipment.
Second, plug in power to modem, let all the lights come on and boot up
Third, plug in the router power and let that boot up and the lights come on
Fourth, Plug in each pc to the ports labeled 1-4
The WAN port should be connected to the Modem also.

ok, lets test the first obvious things. keep in mind that i'm not trying to be insulting at all. i don't know if my words may come across that way, but that is not my intent.

have you unplugged both the modem AND the router, connected them, THEN powered them on? the modem in particular may need to be unplugged for a time varying from 10 seconds to 60 seconds.

is the cable good? try using this cable to connect your modem to the computer. try using another (even if shorter) known-to-work cable to make this connection.

if the long cable fails, and the short one works, then that is likely our problem. if they both work great, we keep looking.

please let me know how these tests help you.

Your expert Geokohler helped me fixed the problem and soved it for me. I sent an evaluation giving him a "fixit" rating.

Try resetting the router to factory , should have a button on the back to do this .
you will have to log back into it with the default factory password
see their site for more info.