If your talking about an hp printer my experiences with them is that hp printers are closed units and can not be repaired if your talking about a computer tower open up the side panel take out the 3 to 4 screws an take the attached wires and replace them one by one to the new psu so you know where each one goes the pins and colors are self explanatory. Then screw in the new psu. But like I said if this is a printer and its not under any warranty hp printers are closed units! Buy a new printer. Unless its a huge office one then call your office repair provider.