It cant be a AM2 because you have DDR memory. If its a socket A you could reapply the Thermal compound to see if it helps first and have some kind of air flow in your case and get a heatsink and fan as a last resort. If its a 754 you can try the same thing but as far as a new heatsink and cooler you can get a 754 sempron 64 3400 for like 35 bucks or a 754 Athlon 64 3200 for 36 bucks so buying a new heatsink for a 2800 754 seems kinda of a waste, the 3400 or the 3200 would run faster and cooler than the 2800 overclocked