Twice in the last two days this has happened to my husband's computer. The monitor goes totally black but the power button is orange, so the monitor itself is fine, just not getting signal. The computer is so non-responsive that it has to be turned off at the power bar. It won't turn off or reboot from the usual power button.

We haven't added any devices or new programs in months. Mostly he's working on text files and running Europa Universalis 3.

The computer is a little more than three years old. The power supply is less than a year old -- we had to put in a new one to power the graphics card he needed for EU3.

Does anyone have any idea what's happening and what we can do about it? Thank you!

have you considered the dust?

Considered the dust? What do you mean? Do you mean we should dust it? Do we need to open the CPU or just dust off the fans in the back?

yes you need to open the cpu casing to see whether it is full of dust or not. because sometimes dust can make your hardware behavior strangely.
to clean the dust, take off all component except the processor (if you're not sure you can take it off), and clean it using vacuum (if you have one, or just dry clothes, just be careful not to scratch it). clean up the gold bars on the bottom of the card slot with the pencil eraser.

try only plug on cpu, ram and vga and connect it to psu, is it showing the cmos/bios startup screen? if it is not then:
try taking off the ram and the vga is the computer creating beep sound?
if it is then the mb and cpu is ok, test your ram and vga in other computer to see if it is working.
if the cpu+mb+psu is not creating beep sound and the fan is not working then the psu need to be checked...

if somehow you manage to see bios screen then:

check the temp (you can use the bios) to see the temp of the cpu and motherboard, is it normal?
last, you check out the dc output of your psu (in bios) to see if the output is also fine.

I'm not an expert but I seriously wouldn't use a vacumm or a cloth.

You need to use compressed air or a new clean paint brush.

Using a vacumm could seriously damage your hardware and a cloth will only leave more lint and dust behind.

yes you are right, using compressor is the best one...
i guess i'm too used to mine using special vacuum, it's small one using usb as its source of power, it is not generating heat, so it is ok for cleaning component (it also have brush extension)

brush is ok, but make sure it is not too hard...

Thats sounds much safter, I had nasty images of this lady with Henry in her system case! Where did you get that nifty gadget from?

If you want to check the temperature to see if your fan is working correctly, I found Everest home edition to be very handy. Check it out if you can't find it in the BIOS.

it is china made, about 2-3 dollars worth. not strong but enough for cards and keyboard cleaning...
there also a small compressor (you can wrap your hand around it) about 5-7 dollars worth, but must be turned off after 10 minutes of working because of the overheat.

Off to eBay now to search for one! Cheers!

i use much caution ,but use all 3,air, soft bristle paint brush,and vacuum,note vacuum only for lower case and front cover and such