Any leds lit when powered on ? AFAIK the TFTP method is the final resort in that kind of situations. If that doesn't help then contacting local support is an option too. Here's a reference if you...

Original router's power adapter ? Overheating problems ? Observing router logs during the issue...

@timung Read through this thread and see if you are affected by the same problem, I believe the user have successfully resolved that at the end.

@timung Exclamation mark means you don't have an Internet connectivity. DHCP should be OFF for sure. What's the main router model ? You are using 2.4 GHz band for WDS right ?

When you set up WDS following the reference I sent, did you check in (C6) Advanced > Status > Wireless to see the WDS status ? When the WDS status is Run, it means WDS bridging is successfully built.

Probably outlet issue, you could check that. Glad to hear you've fixed it.