monitor randomly goes blank. turn off then turn on restore. computer looks running well

[cxterm]

dell xps 8100 desktop, the monitor goes blank randomly, moving mouse, click keyboard didn't wake the monitor. But the pc still running well and response the keyboard and mouse. I turn off monitor then turn it on, the display will restore back. updating graphics drive and changing cable didn't help. Does it a problem of monitor or graphics card? how to figure out the issue? Thanks!

 

[Kisianik]

You provided so little info.
Do you have this issue just recently, or from the time of purchase, did you do any upgrades prior to this issue?
What is your PSU (power supply) is it original 460 watt? Or you upgraded, if yes, what you have now?
What is your GPU, is it was factory installed something like GT 630 or similar, or you upgraded, if yes, then to which card.
What is your BIOS version? The latest one is A05 http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=R275042
What is your OS, is it 64 bit or 32 bit? Are you upgraded, if it is not Win7?
What is your RAM (memory), are you upgraded?
Well, how about monitor, what it is, Dell?

When answered, please mention if upgraded to for video card and memory.