no say hello to meh idk why

when i press the power button to turn it on i hear the beep but then after a while i still see no os saying welcome i just get a black screen no hdd activity and the only way of powering it off is to unplug it. and sometimes it does power on but then the screen freezes and i can her clicks of movement and the hdd has been reformatted and i can not get in safe mode.