the first time i tried to unlock 4th core few months back, i manage to do it. but then system a little bit unstable thus i disable it back. last night i wanted to try again, and it's doesnt work anymore. it doesnt load anything until i have to remove the battery.

Can someone help me explain what is happening with my cpu? Before this i overclock my phenom X4 955 from 3.2 to 4.2, after run prime95 for about 30min i guess, i close it cuz all seems to work pretty fine, after a couple of day, when i start my pc, it suddently show a blue screen, than i change the speed from 4.2Ghz to 4.0Ghz... Now i try the prime95, but the speed is only manage to go till 3.2Ghz only (i only try for 10min i guess, should i run the prime95 a lot longer?) so i change back to the stock speed which is 3.2Ghz, but i'm confuse right now because when i run the prime95 back, the speed show it runs at 4.0Ghz when it should only go to 3,2Ghz. Is this what overclocking does? I'm still noob  .......

below here the details:

Processor: AMD Phenom II X4 955 Black Edition
MoBO: Gigabyte GA-970-D3
GC:Sapphire HD6850 toxic
Ram: Corsair 4gb
Psu: GX550
Cooler: V6GT

The picture was taken while i run the benchmark test using Prime95.