Macbook bricked completely Was trying to update to the latest version of OS Sierra (10.12.6) and Mac suddenly shut down. 


It gives me question mark on a file when trying to boot. 
Power and then command - opt - R gives nothing, the same question mark. 
Power and then command gives mouse cursor only. 


I have Macbook Pro Mid-2010 (A1278)

What to do next?
If you have another Mac, boot this one in target disk mode and check the disk / repair it. If you have another bootable OS - you can hold option and try booting another OS.

Lacking those tools, you my have to see if you can test the hardware itself 

Run Apple Hardware Test

Your model MBP uses Apple Hardware Test. To use this, follow these steps:


Shut down your MacBook Pro 
Restart your MacBook Pro
Press and hold the D key before the gray startup screen appears.
After a while, Apple Hardware Test (AHT) will start.
When prompted, select your language and click the right arrow. 
When the AHT console appears, you can choose to run Basic tests by clicking the Test button. However, I suggest you select the "Perform extended testing" checkbox before you click the Test button.
Your test results will appear in the window in the bottom-right of the console.


Note 1: The extended test will take some time. Take a note of the results and report back. 

Note 2: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.