CPU temperatures are erratic and skyrocket

I run an AMD Phenom II x4 965 Black Edition Deneb, and until I got Windows 8, my temps and everything were fine. As of late, my CPU fan (it's the stock one) won't speed up when the temperatures start to rise, despite the fact it used to. I'll get up in the 50c range just while on a browser with a couple of tabs open at times, and get to critical temperatures while play games such as Medal of Honor: Warfighter. I've ordered a new CPU cooler, a Cooler Master Hyper 212 Plus to be exact, and I've got Arctic Silver 5 thermal compound already. Is there something wrong with my stock fan? Or is it something like a mobo issue? I've been extremely frustrated by this whole situation, seeing as I've only had it for about 2 months now. I'm desperate for help, I can't find any straightforward answers elsewhere. Also, my exact temperatures are the lowest being 34C for all 4 cores, and 59C on all 4 cores, just by browsing websites with multiple tabs.