hi,
i meant pressing on/off button,the phone blackout to be in standby mode,supposedly i need to press on/off button again,to wake up the phone, thinking it has freezed/hang,i press hold the on/off button (simulate scenario of power on the phone) and the phone still do not wake up. untill i take out the battery and place back into the phone.the phone is able to powered on.

however yesterday i encounter this again when i put the hp to blackout/standby mode
thus,i observe and saw that,if,i do the following steps, the phone is ok
1) Press on/off button- screen blackout
2)press on/off button again -screen lights up with a slider at the top
3) press on/off button again -screen blackout mode/Or leave it be, the phone will auto blackout
4)after 1 night, i press on/off button this morning,phone able to wake up
to the screen with slider at top.
But to observe,when charging the hp, the screen will not blackout.