I've relatively not that new on Android rom flashing. I've flashed my HTC Sensation & Galaxy Tab 2 but on this Samsung Galaxy S3 I'm really starting to get a headache.
So, this is what I've done.
Phone was stock with Android 4.0 Originally Vodafone Spain.
Flashed CWM-Based Recovery v.220.127.116.11 + Root Successfully
RootBox-JB-i9300-V3.7.1 ROM + Gapps / Result=Boot OK and Crash after choosing language/Setting Wifi jellybam-5.2.0_i9300.STABLE + Gapps / Same Result Paranoid Android 3.0 + Gapps / Same Result Cyanogen Mod cm-10.1-20130219-NIGHTLY-i9300.zip + Gapps / Same Result
After all this trys I've searched the web and found Original Firmware/Rom from Vodafone for this model with Android 4.1.2 (Aprox 1.3GB Size) flashed it with Odin and Surprize! Phone doesn't crash.
I've suspected that it could be the phone's locked status so I Unlocked it to work on different mobile service operators.
However after flashing recovery + root this time with this toolkit, I'm having exactly same results as before: Sudden Crash when OS is loaded.
At this point I'm being kind of forced to ask for help on the internet because I really don't know what else to do.