Are you writing that pressing and holding the power button for the usual 4 to 10 seconds does not power it down? If so the diagnosis is grim.
However try the usual generic reset of removing the power cable, then press and hold the power button for 60 seconds then release, apply the power cord and try again.
My daughter's computer is not working it is a HP with windows 7, model # p6533w. The power button will not turn off and the monitor goes into power saving mode but I can hear the computer running. I brought the computer home with me to hook it up to my outlets and monitor to see if it would work. It does the same thing. My computer is the same as my daughter's and it works just fine, no problems. Have any ideas as to what is wrong. Please help.