Want to upgrade CPU From 2.80 ghz intel (R) pentium(R) D to above

[umer_saeed]

My PC specs
intel(r) pentium(r) D CPU 2.80ghz 2.80 ghz // (2M)
but I wanted to upgrade CPU and I do so.
I upgraded to 3.40ghz 3.40ghz (4M) but the speed is the same or the I think slow than before :/
Why is this so? And what should I do? Should I replace this to 2.80ghz again or not?

 

[Elysian890]

CPU models? motherboard? power supply? it might help

 

[umer_saeed]

CPU models? motherboard? power supply? it might help

Motherboard:
Manufacturer Product SerialNumber Version
Dell Inc. 0H086H ..CN4294089P03XY. A00

Processor:
Intel(R) Pentium(R) D CPU 2.80GHz 2.80 GHz


Operating System
Windows 7 Ultimate 64-bit SP1
CPU
Intel Pentium D 945
Presler 65nm Technology
RAM
4.00GB Dual-Channel DDR2 @ 399MHz (6-6-6-18)
Motherboard
Dell Inc. 0H086H (Socket 775) 99 °C