Hi..
I dont know very well how to unlock a SE...but, my k800 "died" sometimes and I succeed to fix it..
Let the battery charging for 2 or 3 hours, better if u have an universal charger.
Take a look in download secction (Top Sony Forums) and find the corrects FS, Main and CDA
You said that u want greek language...so u must use this CDA(Custom Files) --> MEDITERR <-- (the list of al languages are here (Top Sony - Languages Description ) and all the CDAs (Top Sony - CDA List). So, find the "HB1-06_Gen_CDA102568_4_R5A_GENERIC_MEDITERR" in the download section!!!

Try at least to "READ FLASH" with the Setool2, look and find what CDA is yours.
In the download section there's the W580_R6BC002_FS_MEDITERR_RED52 and W580_R6BC002_MAIN_GENERIC_LA_RED52, but I think that this R6BC002 is an old version, so find out which one is better for your W850

Hope it works
\,,/