When I turn it on, it shows the Apple logo and starts loading up to about 50%, then the screen turns black. Running the hardware test shows this:
Alert! Apple Hardware test has detected an error. 4MEM/61/40000000: 0x79d53990
Running the system file diagnostics shows this:
What error is that? How can it be fixed? I don’t have a back up and can't risk losing my data.