What operating system do you have?
What happened prior to the issue? Did you do an update/ installed a new software in your computer?
Try to boot to safemode:
1. Turn your computer on and tap on F8 before the splash screen appears.
2. You will get a black screen that says Advanced Boot Options. Choose Safe Mode with Networking.
3. If the issue does not reoccur there, the problem might be related to the video card driver. Uninstall the video card driver:
a. Click start, right click on My Computer. Choose properties
b. Go to Advanced tab and click on device manager.
c. click on the plus sign beside display adapter.
d. right click on the video card driver found there and uninstall. It will prompt you is you are sure you want to delete it. Click yes.
e. Then restart your computer. Boot to normal mode (just let it boot and do not press anything as you boot the computer)
The issue should not be present in Normal Mode but your screen resolution will be very different (bigger). Download the correct driver for your computer from the links posted below:
video driver 1
or video driver 2