Did you replace the processor or is it the one that came on your model? I found an old post that lists compatible processors and info about the heat sink-- 

https://www.dell.com/community/Desktops-General-Read-Only/Dell-T7400-cpu-upgrade-question/td-p/4550597

The S SPEC and STEPPING for DUAL CPU must match EXACTLY.

The Following processors are supported.  Harpertown LGA771.

There are 2 heatsinks for the Precision T7400.

FN654 - Heatsink for 150W CPUs
FD841 - Heatsink for CPUs below 150W

 

https://ark.intel.com/content/www/us/en/ark/products/34446/intel-xeon-processor-x5450-12m-cache-3-00-ghz-1333-mhz-fsb.html

Supported Processors are

https://ark.intel.com/content/www/us/en/ark/products/codename/26555/harpertown.html

X5260	L5410	E5440
X5272	L5420	E5450  C0  SLBBE/SLASB
X5450	L5240	E5430
X5460		E5405
X5470		E5410
X5472		E5420
X5482		E5472
X5492		E5462

 

MaryG, thank you very much for your time!

The I bougth the T7400 just like is, I didn't do anything. I'm just trying to make it work better. I decide to buy a Xeon 5450.

Again, thank you very much!

Speedstep, thank you very much!

I'm going to buy a Xeon 5450, and let you know!

Thks!!