It's a heatsink
A sink is a place that makes things dissapear or move away, like a sink hole.
865 PE is the chipset, and not the actual brand of board.
You could remove the old heatsink, clean up the CPU, and install a new aftermarket cooler if you like. Be warned that the motherboard is getting old and may not work much longer.
A computer that is rebooting could have a bad power supply, or simply be dying as well. Or it could be dying RAM.
Here's a few ideas:http://www.newegg.com/Product/Product.aspx?Item=N82E16835100010
Arctic Silver ACN-60ML (2-PC-SET) Thermal material Remover & Surface Purifier - OEMhttp://www.newegg.com/Product/Product.aspx?Item=N82E16835186134
ARCTIC COOLING Freezer 7 Pro
Comes with Thermal Interface Material (TIM) pre-applied, so is easy to use for the novice.