Main U-Verse box will not turn on even though there is power

Equipment fails.  You can call CS 1-800-288-2020 to request replacement equipment as a self-install.

If this is your DVR, be aware that when replaced, you will lose your recordings but not your schedule.  You have 60 days to return the old equipment via UPS/FedEx.  You will receive an email with instructions.

I'm not sure what you mean by "Main U-verse box?"  Do you mean the DVR?  Does it have any lights at all?

Do the power adapters for your other receivers fit your DVR?  Have you tried switching them to check to see if the problem might be the power adapter?  That might save your recordings, but you still have to swap a receiver (AT&T won't just send your a power adapter).

Let us know what you find out.

Yes, it’s the ethernet connected DRV box.  I swapped receivers and one of the wireless boxes worked on the same power adapter.  

I’d be careful interchanging those adapters, check the ratings for both.   

I’ve experienced the problem you described in the OP.  It required my having to force a reset of the box.  Plug and unplug the DVR 3 times.   Allow a few seconds between each.   On the final plug-in the box should start with gray gear and will take several minutes for the firmware to download.   Eventually the standard Uverse screen will display and your box should be functional again.  Your recordings should be intact as well.  

Yes, the DVR draws another amp or two, but at least for a quick test, I'm not too worried.

gr8sho's NDR procedure above works best if the DVR will at least come up enough to display the three dots on the television (indicating it's time for the next power reset).  If you're not getting any lights at all, then sounds like the motherboard is shot and it's time for a call to AT&T Support for another DVR.  If you swap, you'll lose the actual recordings, but your schedules (series, etc.) going forward are preserved in the cloud.

I’ve recovered a box that looked otherwise dead.