Removing a PSU

Sometimes the 20/24 pin main lead from the psu to the mb can seat very tightly like you are experiencing. plastic inserting in plastic and heat can make the plug a tight fit. Be sure to apply enough pressure on the little clip to dislodge it from the ledge holding it in place. Then pull up evenly with as much force as needed to unplug the 20/24 pin lead.

Thanks I got it out but I now have another question. The PSU I bought is a 24 pin and I counted and my Mobo does use a 24 pin but the PSU I took out is a 20 pin. What do I do? Could my computer have been damaged from using the wrong amount? I did not build this PC so I was unaware until I opened it and removed the cable.

If the 24 pin lead from the new psu matches the MB main power socket, just plug it in. the extra 4 pins are additional power for the 12v. 24 pin was designed to provided extra 12v power for SLI systems initially. No damage should have occured nor should damage occur using the new 24 pin lead.