thanks! And more details

It is a Toshiba computer, MS Windows XP operation system. I called the Toshiba tech. support who said that it might be due to the OS corrupted, so I reinstalled the OS, yes, by connecting the notebook to a different monitor. That worked for 2 weeks, and then black out again. Actually it is not entirely dark, but very dim.

In the past, the darkening screen occurred several times, and after I restarted the computer, the screen came back, then in a couple of weeks, the display became dark permanently.

I think it should not be hardware problem. Could it be caused by some conflicts between the video driver and some other softwares I use? I've cygwin and Winshell
installed recently.

Thanks for help!