Memory Mystery and motherboard temp

Hey all, i've recently built myself a new pc. I am a Student currently studying computing with a lot of experience, however have never ran into this kind of problem before. I order a 2GB Pc5400 stick of memory and the computer is registering it fine, however there is another 1GB installed. I found that they are mostly likely incompatible with each other, however is the niche for some reason after installing Windows vista service pack 1 the computer is now registering the 3GB of ram, yet the Bios and other applications do not recognize the extra ram. In order to check i wasn't duped and given false memory i removed the 1GB stick to ensure it was a 2GB stick and in fact it was. A bit of a relief mind you since it took ages to arrive lol. Anyways i just don't understand this. It's very strange.

Also just out of curiosity I was wondering if anyone knew the appropriate board temperature that the GA-P35C-DS3R should be running at because it just seems very hot when i touch it and on top of that Sissoft Sandra claims that the board temp is currently: 38C Is this an acceptable temperature for the board? I'm going to get a psu with an extra fan and will be putting in another fan in addition to the fan on the side of the case and the one on the cpu.

In addition i was wondering if the pc maybe under powered it boots and runs fine, so i'm assuming it's fine, i'm going to replace the psu anyways, because it's very loud lol esp when watching movies on the machine.

The Pc Spec is as follows:

Operating System: Windows Vista Service pack 1
CPU: Q6600 Intel Quad Core 2.4GHZ
Memory: 2GB or 3GB ( depending on if this problem is fixed)
Motherboard: Gigabyte GA-P35C-DS3R
Hard Drive: Seagate 500GB
Graphics: Nvidia GeForce 8400GS 512MB DDR2
PSU: 450Watt ATX