OK. Funny thing. I opened the xbox and reallign the mod chip (the matrix modchip is not soldered, just alligned and screwed in). Apparently, the dip switches trick I used to "repair" the bug put it in a better position because of the pressure it put on the chip. But now, after trying a lot, I alligned it correctly and it works fine. It's just weird because for more than 1 year I've brought my xbox to friends's houses and had no problem with that. So I guess that matrix owners need to reallign their chip once in a while.