>> try reinstalling the vga drivers, get the 10.5 ati catalyst. also check your gpu temps
the halt happens just as window logo is about to apear and sometimes just after starting the PC so I think is not a driver issue.
>> have you tried with another 6pin power connector cables?
yes I did although only changed 1 of the cables, I`ll try 2 new cables for double check.
>> Try boot on safe mode
tried, same bug :S
>> so you make sure your PSU supports 30v on 2x6 pin
yes I have 2x6 pins, but I wish I could somehow measure the electric current in the cables to make sure they give the correct power.