Samsung S3 stuck on first ¨page¨ (before the logo), how can I fix it?

[AC Question]

Samsung S3 stuck on first ¨page¨ (before the logo)

Hey guys, got my 2 year Samsung Galaxy S3 GT-i9300 that suddenly turned off and won´t start. It gets stuck on the page that says in white letters GA....etc before the logo with the samsung blue thing circling appears.

So, tried to go into safe mode. No luck.

Recovery mode:
green android dead on it´s side, red sign and...
e: failed to mount /efs (no such file or directory)
e: failed to mount / system (nsfod)
#Manual Mode#
Applying Multi-CSC
same failed to mount but with system, then cache and then cache/recovery

Did a wipe cache partition and this appears:
e:/format_volume: make_extf4fs failed on /dev/block/mmcblk0p8
Cache wipe complete.
e: failed to mount /cache (block device required)
e: can´t mount /cache/recovery/log
e: can´t open /cache/recovery/log

and lots of similar lines.

Now...I´m not an expert, don´t have my phone rooted. I just want to know please:

1) how can I recover my data on my phone (before I try WIPE DATA/FACTORY RESET)

2) step by step instructions to recover my phone without turning it into a brick.

Many thanks!
Nico