Trying to overclock an i5-2500k with a Gigabyte P67

Hi, I've been trying to overclock my Sandy Bridge for a a while now, but alas keep failing.

I am fairly new to this, but have some understanding.

I am pretty much following this guide, but keep having problems.

After I set my clock and voltages, I go to restart and usually end up getting stuck at the windows logo screen, and having to manually restart. I've tried making the voltages higher, lower, and tried changing the clock speed as well, but no luck.

Can anyone help me out?

Hey man, can you tell me what bios you are using?
Different bios' need slightly different settings