My ps3 is hardly to power on!

hi all, i have a problem with my playstation 3 (2008 version - CECHL12)

It is very hardly to power it on, the most percent: when i press the power button, the green light is on and it say" beep " one time, but it cannot power on, my tv display "nosigal", and i cannot turn it off with power button. It just turn off when i push the button at its back.

if i press power button in long time ( about 5 seconds), it will power off with two beep.

some time, it works normaly. but when it powers on, i dont see any notece as " your ps3 was not turn off corectly ..." and my ps3 run normaly when ever i turn it off

the same issue if i use the ps button to power it on

how can i do to fix it? thanks for your help