It's difficult to say without seeing the laptop. There might be different reasons for the screen to go blank.

1. Power Management: Disable screensaver, supend, hibernation and other sleep modes. Make sure laptop is running on AC power supply.

2. Driver problem: Update the latest driver for your display card.

3. OS problem: Perform System Restore to an earlier date. Start Menu > All Programs > Accessories > System Tools > System Restore.

If System Restore fails try redoing it in Safe Mode. After powering your laptop press F8 multiple times to start Vista in safe mode.

If you cannot do system restore then perform clean installation of Vista by formatting your hard drive.

4. Hardware issue: Might be problem with the display adapter or might be some kind of loose connection between the MotherBoard and the LCD unit.

Good luck!