That's it! I couldn't take it anymore! When I finally managed to enter Windows in Safe Mode I removed the graphic card driver and installed my old one yet again!!
I'm now sure that the motherboard is the problem, I must get a new one eventually, but if I do it will be PCI-E and my graphic card won't be compatible, but I have to return the one I bought anyway...
With luck I'll find one comaptible with my Athlon AMD 64 3000+ CPU...
I'll try to manage with my current motherboard for as long as I can...