Here is what I am thinking CodyC.
If 52c is to hot at idle, then something is drawing an inappropriate load or has to much voltage and is manifesting itself as heat (considering your heatsink and cooling are adequate).
It may be a bios setting. I would take out the battery and switch the little default jumper the mobo has and then put them both back. CAUTION: THIS MAY CHANGE YOUR DEVICE SETTINGS! But, if you never fooled with the bios before then stock is probably OK for you. Save your files first!
You may have a circuit that is shorted enough to draw an undue current, but not enough to start things frying. At least not yet. If this is the case, this is not good. It means chasing down the culprit. What is drawing the current? Is it the video card? Is it the sound card? Is it some little who knows what the hell that is on the mobo?
Rosco maybe be right on. It may be bunk mobo capacitors, or such.
If I were you I would pull all the cards, drives, and whatever you can to get the system down to as simple thing as it can be to access your bios for temp readings. I'm guessing here, but I think you need a psu, mobo, processor, at least one stick of ram, and a keyboard to start the computer. If you do this and the computer runs cool, you are on your way. Basically, you are playing a detective game at this point.
As far as a 300 w psu goes, I can't imagine such a small psu. However, even though it may not be enough under load for the computer, I imagine it should be no problem running your computer at idle. Besides, if the psu was lacking power, I can't see that making a heat issue; I would say quite the contrary. Also, your voltages are steady for the cpu, so I am hoping that is an indication your psu is at least capable to start things up.
Disclaimer: If things get hairy and start frying don't say I told you what to do!
Good luck.
Clutz