HP DC7700 with E6700 CPU weird problem?

Hey guys i have a strange problem. I have an HP dc7700 and recently i upgrade my CPU from E6320 (1.86ghz) to E6700 (2.66ghz). The problem is that when i play Bad Compnay 2 on Medium-Low settings my Cpu fan is running reallt fast. But when i play other games on the Highest settings my cpu fan is stable..I run the CPU-Z and i got the following:

Core 0: 1592mb 266x6 and voltage is 1.300v

Why my Cpu is not running at 2.66ghz and it's underclock to 1.6ghz(1592mb)???
Also when i installed the CPU i used my old fan becasue it's bigger than Intel's but i didn't used any thermal paste because my fan has a little bit of it underneath. Please someone help me cause it's to annoying hearing the fan like an airplane engine!
http://dailydigitaldeals.info/wp-content/uploads/2012/01/11/20/buy.gif
Specs:
HP DC7700
E6700 2.66ghz
9600gt 512mb GDDR3
bios version 786E1 v1.08
3gb ram

Thanks!

 

Is that 1592 MB or 1592 MHz? One is space related, the other is frequency related.

Whenever replacing a CPU, It's imperative that the surfaces be cleaned with 90% isopropyl alcohol prior to applying a thin coat of thermal paste to the surface of the CPU. This is essential for the proper transfer of heat from the CPU to the heat sink.

 

General Information

I believe that most Intel CPUs have thermal throttling - their computational power is turned down if they become too hot, in order to protect them from overheating. This may be why your CPU is not running at the rated speed and yet is apparently at 100% with fan on maximum.

Try installing CoreTemp to see the temperature of your CPUs. Both cores should be below the indicated Tj there and that number should be 60.1C (http://www.cpu-world.com/CPUs/Core_2/Intel-Core 2 Duo E6700 HH80557PH0674M (BX80557E6700).html#specs)

You should certainly take mdonah's advice.

Dumb_Question
23.May2014