well 1st off. 1.6 r only model that u cant do a tsop flash to, due to the fact there is no tsop on the board anymore n the bios is loaded from diff location that isnt writable.
2nd thing, if ya believe its not workin correctly due to heat, get some extra coolin cuz if its not bootin the chip from heat then the xbox is too hot.
3rd, i'd say check ya installions, tap all the points with soldering iron so all the solder melts n then take it off(like only a sec or 2 on each point) incase ya got a cold join.
cheers

Edit. would do 3rd thing i said b4 lookin at extra cooling