Can't overclock my 2500k

I'm having issues overclocking my intel i5-2500k on my Asus P8Z68-V motherboard. I went into bios to try and manual do it, and I kept getting BSODs even on the most meager of overclock settings. I try using the utility program that it comes with and it doesn't do much either. Whenever I use AI Suite II and go to the clock frequency on my CPU, it shows 1.6ghz but it will fluctate to 4.2ghz for about 1 second. Help?