PSU= Power supply Unit.
HSF= Heatsink/Fan
OC=overclocked
50 degrees C is well within operating temps but it is not normal for a CPU with a HSF like that. My OCed 2500+ @3200+ speeds gets to 52C max with the horrible retail heatsink.
You're processor is not overclocked if you don't know how to overclock. And I doubt you would want to underclock the processor, but if you're motherboard supports it you can go into the BIOS and do it. (usually you press the "Delete" key right as your computer turns on to get into bios. If it is another key there should be directions someplace on the screen. *i'm also not talking about the windows startup screen* it is the screen when you first turn it on, ususally a brand name of some sort for the motherboard or computer company.)
You can change the temperature protection feature in the bios to a higher temp to keep it from restarting.
Try Speedfan instead.
http://www.almico.com/speedfan.php It might be able to help you with your CPU usage problem.
Did you use thermalpaste or a thermalpad when you put the heatsink on?
Have you cleaned the heatsink and any fans in your system lately?
You're problem could be airflow over the heatsink and through the case itself. How many fans do you have running? I would suggest making sure all of you're cables are pushed to the side as much as you can and try to keep the inside of the case as open as possible so air can move freely. And more case fans will most likely lower your temps.