Overheating

I have a Dell Dimension 4700 about 1 1/2 years old, ever since i have found a program to check the temperature (SpeedFan) its been over heating but i've noticed that my Dell has a fan located in the back of the case and has a plastic cover that directs the air flow through the heat sink. It seems to me that the fan isn't working. I have done some upgrades but nothing to overheat the processor. Should i install a new heatsink with a fan attached to it? Please Help

P.s. The Temperature is running around 140 to 160 F

 

It could actually be the program...

It seems to me that since you installed the program, and been having issues with the pc overheating, that either the program is malfunctioning, and giving you a false reading, or it might be causing the overheating.
Did the overheating start right after you installed that program?

 

No i had the program since i had the computer, but the overheating was 6months after having the issue, i figured the problem out thoe, my max output on my power supply is 305 and with all the upgrades (i calculated what i need) i need 400 Watts of power... so im going to upgrade my computer with a 500 Watt power supply and just incase im going to buy some fans for it, and maybe some cool ass LED lights just for fun... thnx for the help