r7900 bricked after firmware update

Greetings,

If the power button never stops blinking, either the router did not fully boot, the FW is corrupt or there is an issue with the power supply.  Since you tried to update the FW and have tried resetting, a bad or corrupt flash is likely. 

Its easy to fix.

Grab a copy of the latest FW and unzip to your desktop.  Always upgrade from a PC connected via wire.  The wireless thing can/might work, until one time it doesn't and here you are. 

Here are the instructions for TFTP reflash

TFTP reflash is simple I promise.  However it relies on timing and correct command usage.  Don't be discouraged if you have to try it a few times before you get it. 

There are plenty of us here who can help if you get stuck.  Also, don't worry, you won't hurt the router by attempting this operation.

First boot.  Be sure to disable Auto-Updates..  this will be the very first screen you see after flashing has completed successfully.