Try a different monitor, it may not be an issue with your x51 after you tried the things you mentioned above. If you cant try a different monitor at least try to switch the monitors channels, hdmi, dvi etc

And try to unplug the monitor, leave it unplugged for a couple of seconds. Start it up again and see what happens.

If none of the above work call AW tech support...

You can also try a different cable or connection, try the onboard HDMI in. If none of that works please send us an e-mail with your tag and phone number along with a brief description of the issue that you are experiencing and we will get back to you as soon as possible.

thanks i tried the hdmi and i got my computer to display but now it just keeps loading bios everytime i try to start windows normally

Hmm, can you start in "safe mode" at that boot up prompt to see if it gets into windows that way?  Also give support a call at  1800-alienware so they can walk through some troubleshooting with you or Luis can help here.

What if the screen just show black screen (no signal black). And there was not even a beep. Yesterday, I accidentally "upgrade" the bios version from A03 to A02. Then the computer just show the black screen. No beep, no bios option... I feel miserable.