Replacing a PSU- 20 pin STUCK!?

Hi guys
I am trying to replace my current psu with a higher wattage version. This is my first time doing this type of thing, but I've done my research and felt pretty confident about going forth with the job on my own.

However, after unplugging everything, I got to the 20 pin connector, and it will NOT budge. I'm well aware of the little release lever, I even tried to pry it off in attempt to free the plug, but that doesn't seem to be the problem. The plug will just not come out no matter how hard I pull, as if it has been glued in place. My computer is working fine after putting everything back together, so surely it's not fried or melted to the thing?
Don't know if it matters, but I'm using an HP computer.

Any help greatly appreciated!

 

If you feel confident, try removing all the devices from the motherboard, and taking it out of the case. It is easier to work on. Take note of where the front panel connections go and the rest is pretty simple. And yes they can be tight.
For tips and pictures try tomshardware.com

 

I use large needle nose vice grip pliers. Set the tension enough to hold the connector, but not so tight as to crush the connector. Make sure the looking clip is unlocked, and pull straight up with the pliers. The extra leverage by having the pliers attached is much more than you can apply with your fingers.