First go to your matrix's webpage, this is by either typing in the IP address into a web browser or by going to gotomymatrix.com 
 
or

Then your URL should look something like this:
You will need to remove everything after the / like so:
After that you will need to type the following and press enter afterwards: system/errorlog
You will then get the full error log which should look like something like this:

Then either right click on the log and press "Save As" and save as a text (.txt) document, or highlight (Ctrl + A on Windows) and copy (Ctrl + C on Windows) the entire log then paste (Ctrl + V on windows) into a blank notepad document and save.
Save the document and then send to us for diagnostics.