Well Dan......
Go into BIOS, see if you have any options such as "AMD Cool n Quiet" or "Intel Step" or something, that will automatically control your fans.
Think about this, if the fans are already too loud, they're operating at full speed. So, what are we going to do in BIOS to slow them down that won't cause the CPU to overheat more?
Your extra RAM problem may either be forcing the Motherboard to run in single channel (although it isn't an extremley noticable performance drop) or it's the CPU having to seriously throttle itself making you think it's the RAM.
The OP states that he only has a 1GB module installed. Therefore, the board ALREADY must be in single channel mode. This is because you can't possibly run dual channel RAM with only one module. So, by adding the second 1GB module you could only force dual channel mode. This of course assuming you put it in the correct socket, and it is compatible with the DIMM that's already in the machine. And face it, If they were that dissimilar, the computer might not boot.
@vishsolanki Did this problem just start?
Pentium D CPUs have a very high power requirement, up to 130 watts TDP. As a result of this they tend to run quite hot even in normal operation.
If your CPU is "throttling back" or shutting off, the high fan speed is saving the thing from perhaps burning up altogether.
Clean out the machine as the others have suggested. Learn about Anti staic precautions before you put your hands inside the case. At minimum ground yourself to the computer case and try not to contact anything inside until you buy a proper anti static strap.
The thermal material or grease, or what is also know as thermal compound, may have broken downm or is not installed correctly. (between the heatsink and the CPU). Also there is the possibility that the heatsink has come loose. This can happen with Intel push-pin type mounting.
You may also have an application "hanging", or some sort of "malware" in the machine causing the CPU to operate at or near 100% constantly.
Pull up "Task Manager" (Cntl, Alt, Delete), then click on the "performance" tab, and observe the green bar graphs which indicate what percentage of the CPU is being used, then get back to us.
You might have to opt for an aftermarket fan as Robin has suggested.
i just changed the cooling system to something more better, and made sure i selling to someone who doesnt use alot of power.
You can check out this Wikipedia page that suggests using a "Pent D" in a 945 board disables hyperthreading
http://en.wikipedia.org/wiki/Pentium_D.
Also, people like you are the reason I don't shop on Ebay.
