Hello and thanks for your answers.
I've tried different PC's and USB ports and the problem persist.
I have the latest garmin drivers and runing windows 8.1
AV was disabled but no luck there
I will try QuickCure 3 and cleaning NV memory but i'm still reading a bit so i'll take the night to do so. I'll tell you later if it worked (i hope it does :D)
If it helps, here's the picture from the diagnostic menu in the Nuvi:
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