Yes indeed, only one pc connected does freeze too. I did'nt try without internet, i'll check later.
I flashed firmware from recovery mode, I read the sticky before =) .
Setup always from scratch, never from saved config.
Theories:
Maybe the router "somehow" is overheating. It's summer here and temperatures are over 36ēC sometimes.
Maybe the power supply went bad.
I'll try to call D-link after doing some more testing at my friends place, who has a Dir-600 too.
I refuse to not know what's wrong with it.