Why won my Hewlett Packard HP Pavilion 7955 Desktop Turn On?
It could be a power supply problem. You can try getting a new power supply and installing it and see if that was the problem. If it still won’t turn on you can return the power supply. If the computer is under warranty call the manufacturer. Also be sure that the monitor is turned on and that the connection to the computer is tight and that you have connected it to the graphics card connector.