CPU Overheating

Hi, so I recently had to replace some hardware in my mom's PC, specifically the motherboard and the heatsink for my cpu. One problem that I'm having is that both of the fans are running at what seems to be max speed, although it's not very loud at all, so it's not my main concern. The primary concern is that my cpu will go up very high, to about 80 degrees Celsius, after maybe an hour of casual use. It doesn't seem like there's a pattern. For example, I was watching netflix, had 10 tabs open, and was playing a game, but I was staying around 45 degrees, but when I just closed everything down, after 10-15 minutes of watching youtube, my computer gradually jumped to 80. Does anybody know if this is possibly a problem with my heatsink not working well with my board? My old heatsink wasn't compatible with this new one, had to get a new heatsink. I even tried taking off the heatsink, clearing the cpu and heatsink of paste, and reapplying the thermal paste.

EDIT:

Heatsink

Motherboard

Processor:
AMD FX-6200 6-Core @ 3.8 GHz

yeah.. that cooler is a little anemic for the 6 core. it says in the product description it handles up to 90 watts, the processor is 125 watt cpu, you do the math.

alot of people use this one with good results.

Shoot. Good thing I only spent $12 on it.

sorry that seems to be sold out. but just pick up any tower like heatsink that's similar to that one, you will see better results. but to be on the safe side try to find the wattage disspating specs at least above 125 watts

Cool, can you recommend on that can fit in a micro atx case and is compatible with that motherboard? I need some suggestions, I'm not so good with finding that stuff out. Thanks.

what case do you have?

I can't find it, it's an older hp case though from like 2004. The dimensions are 16 inches for length, 7 inches width, 14 inches height.

http://www.newegg.com/Product/Product.aspx?Item=N82E16835705069&cm_re=low_profile_cpu_cooler-_-35-705-069-_-Product

something like this? what's your budget? you might be able to go lower but i dont have a tone of experience with low profile coolers

Try this.. They are good up to 140W
http://www.newegg.com/Product/Product.aspx?Item=N82E16835118141

Really good passive heatsink