Your sempron is Socket 462, you wont find any shops still selling aftermarket coolers for it because its 4 generations old.
Also its not worth spending any money on a cooler because the most you could overclock that is probably 2.1ghz which wont be noticeable.
Save a bit more and do a system overhaul. Buy a new AM3 motherboard, CPU and ram.
You can transfer your old harddrives to the new one.
You will need at least $200 to build a decent AM3 dualcore.
I sold my dad's old sempron 2500+ for $35 a few weeks ago, that should give you an idea on how much to sell your pc.
CPU: Phenom II X4 B55 3.3 Ghz
Motherboard: ECS MCP61M-M3
Graphics Card: Sapphire HD5670
Memory: 4GB Kingston DDR3 1333
02:06 PM by