PERFORM THESE STEPS before posting about POST/boot/no video problems!

I have an HP Desktop computer Model P6531C that was working perfectly welle when I shut it down at night and the next morning when I turned it on nothing happended it just sits there no post no video and my monitor just say no signal . I tried all your suggested steps . I installed a new video card stil nothing but all lights are on and the psu is good memory also .

Please help me don't understand what is going on neither how to fix it

Thank you

Roly