Computer wont start!!!

Hello, I have a lenovo laptop and for some reason the lap doesn't start up sometimes. When the laptop hybernates or shuts down it doesn't turn back on. When i click the power button, the power light comes on, the battery light works, and the wifi light works but the hard drive light doesnt come on...the screen is blank, i can hear the cd rom drive turn, and the fan sometimes works...i usually try to drain the battery and then restart it and that works sometimes...don't know whats the problem...