Please tell me which motherboard i need to buy for phenom x2 555 be.
The newer boards are the 880G that have the physical unlock switch. They are around $100. You could always get the last gen board which is a 785G, but you need to unlock the cores through the BIOS. I think those boards are around $75 on Newegg. http://www.newegg.com/Product/Product.aspx?Item=N82E16813131595.
I believe the setting is Advanced Clock Calibration. You have to enable this. The only downside is you can not monitor the temps on an unlocked chip. Which is no big deal if you don't OC or OC much.
Just remember not ALL will be stable after they are unlocked as they do not test the chip with unlocked cores. SO every once and a while it won't be stable and you are just stuck with a great dual core. However, my buddy builds PC's and I recall him saying he has only ever once ran into this.