Toshiba satellite L505D 6000 sometimes won't boot up

Hello,
I have a laptop Toshiba satellite L505D 6000 the problem is sometimes it boot up and sometimes it won't even though i turn it on for many times it doesn't work to boot. after a day i try to turn it on and it works normally as it doesn't have problem but a couple of hours i start it up it also doesn't boot again. lately the problem when i sleep and hibernate the laptop when i wake it up it doesn't work only black screen. and i think the power is on and the hard drive also spin. the same as it has battery .
any one can help me in this problem...

Thanks