can you describe step by step what you did when you installed the heatsink?
and did you put thermal paste on it? if so, how much? or did it come with a thermal "pad"?
is the fan plugged in? any thermal paste residue on anything besides the top of the cpu, and the bottom of the heatsink? are all fans functional?
and the new heatsink should be blowing air towards the back of the case, with the back fan exhausting air. the top fan is also called a "blowhole" and is intended to exhaust, but i havent really noticed that much of a difference in making it an intake. just remember the principle: heat rises: so have intakes at the bottom/front and exhauts at top/back. side panels are also usually best with the fans set up to intake, as it blows cool outside air directly on to the motherboard and its components.
here is the optimal airflow for a computer case (i drew it lol)