This is usually an issue with a driver. You need to contact the machine's maker.
About every 5th or 6th time i put my laptop into sleep mode, the screen shuts off but the hard drive led and all the normal power and hard drive leds keep blinking, especially the "thinking" led, thats going a mile a minute. and it will not stop. the laptop is still on but is unresponsive, it will not finish going into sleep mode and i have to hold the power button down and force it to restart.
Again, the screen shuts off and will not turn back on, the keys are un responsive, and the computer will not finish going into sleep mode.
How do i fix this?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic