Sleep mode or black screen

Sounds like it is going into Sleep or Hibernation mode.
In Control panel go to Power options and see what the settings are.
Getting out of sleep mode is accomplished by pressing the power button once.

This happens with my Acer Laptop too. Make sure the computer is plugged in to a power source and try a forced restart. If that doesn't work, try using the sleep command to but the computer to sleep while the screen is black but the power is on. The computer's power light should shut down, and you should be able to go out of sleep mode by pressing spacebar.

Here is artical I found on how to disable sleep mode on a monitor, this would be for VISTA or 7, if you are using XP it's a bit different. ____________________________________________________________ How to Disable Sleep Mode on a Monitor

Your computer monitor or laptop screen will enter sleep mode after your computer remains idle for a set period of time. You can disable sleep mode if you prefer the screen to remain illuminated. You merely need to change a setting in the Windows Power Management properties box.
Difficulty: Moderately Easy Instructions

1. Click "Start" and "Control Panel".
   

2. Click "System and Security" and "Power Options". This will bring up a new dialog box.
   

3. Click the menus to the right of "Turn off the Display" and set them both to "Never". This will disable sleep mode.
   

Read more: How to Disable Sleep Mode on a Monitor ' eHow.com http://www.ehow.com/how_6953659_disable-sleep-mode-monitor.html#ixzz1CiGFFyLk

Try to go into the energy management settings (by clicking the power mgmt icon in your system tray) and seeing what your sleep settings are. You should be able to customize your sleep settings to do more than turn off the screen.

try using the Fn + F?key (has a graphic of a monitor)F5 or F7 to switch the system from external monitor to the laptop ... you probably have it in presentation mode for external monitor.

When you turn on your laptop do you see the P.O.S.T screen or it just remains blank? and also while booting up do you get any beep sound?
Try to boot your computer in Safe Mode by Tapping F2 (or Del in few laptops) key after pushing Power Button.
let me know what happens.
Askari :)

I've had spotty luck with Windows and sleep or hibernate modes. I would suggest just disabling sleep/hibernate mode. The options can be found under the control panel under power options. While turning off the sleep mode won't help your battery life, if you ask me, it beats having to power off the laptop by pulling the battery out. If you don't want to turn it off, you can try adjusting the amount of time it lets pass before it goes to slee.

Hi,
sounds as if the laptops in hibernation or sleep mode.
Try refering to the user manual regarding the mentioned points.
also try alternating the memory from slot to slot, 1 faulty slot or ram module, will cause the computer not to boot.
Finally, if this is a model that has a ribbon-cable from power switch, to motherboard. ensure it,s inserted correctly/square et,c.

Hope this helps, thankyou for using Fixya.

mike @ Compurepair.

you have trapped it on sleep mode and there is nothing you can do for that. the only way you may be able to fix it is 2 try and unstall windows itself or even taking it to a technician that knows about the laptop more than what you do. (dont take it offence)

test it with another monitor if you things then maybe the LCD has a fault.  Come back here for more instructions