Hello.
Rb750 after upgrade from 3.28 to 5.16 is dead.
Not booting, no link activity on ethernet ports.
Power and ACTivity LED is still ON after power on
Hold this button during boot time longer, until LED turns off,
then release it to make RB750 look for Netinstall servers.
Holding this button , but LED is still ON. Not able to use Netinstall 
RB is out of waranty. The attempted upgrade and I lost him?
Any chance of recovery or RB750 to trash?
how long did you hold the button, and did you press it and then power up the board.
Yes - first hold reset, then power
I hold it 1minute but stil nothing
Try to reset using “reset hole”: http://wiki.mikrotik.com/wiki/Manual:Password_reset
This will reset bootloader and then try Netinstall again.
Unfortunately it does not help.
There seems to be damaged RouterBOOT. But with version 3.28 worked. Probably damaged during the upgrade…
I had exactly the same issue. I found out one of the capacitor’s was blown up on the RB750 (known issue). Replaced it with another one and re-installed with netinstall. It’s working fine now 
Capatitors are OK. Router works with 3.28, but dead is after upgrade to 5.16
Just forget bout it man! it aint gonna work again, i had same case but mine capacitor not burn… after upgrade then its stopped…
We received four used RB750s a couple days ago. All four booted fine and functioned properly running 4.x, so I began the process of upgrading (to 4.17, 5.0, then 5.21, updating the firmware whenever one becomes available). Three out of four made it to ROS 5.21 & 3.0 firmware; one got bricked along the way exactly as described in this thread. After uploading a new ROS version and upgrading the firmware, the reboot simply never completed. All LEDs came on as expected, but never went out. All components on the board look fine, no smoke found its way out of the circuitry. No amount of playing with the reset button or shorting the reset pad has any effect.
Now what: throw it away because of some boot loader mismatch/glitch?!
Hi All,
In the case of Bricked RB750 units, (I personally have a small pile growing by my desk), the problem with us is that the cost to RMA the device does not make commercial sense. The shipping cost to send these back to distribution is too high for the value and so we simply replace the units.
In an ideal world, MikroTik and/or the distributor could replace the units to the resellers without being sent the damaged units (maybe the inside label and a piece of the board as proof of destruction?) but there seems to be no fair way of this working and the amount of ‘bricked’ RB units would probably soar very high in a very short time, to the detriment of MikroTik. It could also be the case that resellers then start to not even bother to re-install failed units but just send in the request for replacement.
When one considers the cost of the basic RB750 unit and the value one gets unless the unit is DOA, unless one sends RMA in volume, e.g. 20 units, it’s just not worth the cost and hassle. If the distributor is understanding and the units still under warranty, one could maybe come to an arrangement for volume RMA but that involves trust which seems to be in very short supply.
In the case of blown capacitors, although bothersome and we bear the cost if unit still under warranty, this is feasable and works fine as a quick fix. Even if RMA would be cost effective, it’s such a quick soldering job that filling in the paperwork or forms would probably take more time and therefore money.
Just my 2c worth,
Rgds,
Mark.