My screen goes blank occasionally when I come here.  But usually I hear myself snoring and it wakes me back up.

bapu
FYI... nothing about their room temp has changed.
 
So is it possible that the CPU fan (which was running when the black out occurred) is no longer powerful enough or has become "unseated" (i.e. CPU thermal grease dried out and needs to be replaced)?
 

Saying the fan is running doesn't tell the whole story. What does the heat sync look like? Is it completely clean or can you see dust on it? If you spin the fan blades by hand with the machine off, do the blades spin freely without restriction? Or do they spin once or twice and then immediately stop?

How about the rest of the innards, how do they look? Clean or dust bunnies everywhere?

Has anything else changed recently? For instance did they get a new computer desk with a little cabinet for the computer tower? Or as I like to call them, a computer desk with its own Betty Crocker Easy Bake Computer Oven.

Also don't rule out the monitor itself. 

JohanSebatianGremlin
Saying the fan is running doesn't tell the whole story. What does the heat sync look like? Is it completely clean or can you see dust on it? 

Clean.
 

JohanSebatianGremlin
If you spin the fan blades by hand with the machine off, do the blades spin freely without restriction? Or do they spin once or twice and then immediately stop?

Spins cleanly.
 

JohanSebatianGremlin
How about the rest of the innards, how do they look? Clean or dust bunnies everywhere?

Very clean, just a little dust.
 

JohanSebatianGremlin
Has anything else changed recently? For instance did they get a new computer desk with a little cabinet for the computer tower? Or as I like to call them, a computer desk with its own Betty Crocker Easy Bake Computer Oven.

Nope same desk, setup for the last 7 years or so.
 

JohanSebatianGremlin
Also don't rule out the monitor itself. 

Haven't yet.

Ran the speed fan util.
 
Something called Temp 1 is listed as 85C with a flame icon next to it.
 
Core 0,1,2,3 (it's a Q6600 CPU) all say 32(ish)C, as is everything else there.
 
Gonna have to go into the bios to see what Temp1 is. Tomorrow night. Working late tonight.
 

bapu
Ran the speed fan util.
 
Something called Temp 1 is listed as 85C with a flame icon next to it.
 
Core 0,1,2,3 (it's a Q6600 CPU) all say 32(ish)C, as is everything else there.
 
Gonna have to go into the bios to see what Temp1 is. Tomorrow night. Working late tonight.
 

 
yep....converting that 85C to F is about 185 degrees F which is not good for the cpu.....basically, the cpu is overheating...
probably needs new thermal paste and just a little cleaning and loving and all should be fine.....
That's what the bios is suppose to do is if the cpu reaches a critical temp,  the system shuts itself down so it doesn't ruin the cpu.

einstein36

bapu
Ran the speed fan util.
 
Something called Temp 1 is listed as 85C with a flame icon next to it.
 
Core 0,1,2,3 (it's a Q6600 CPU) all say 32(ish)C, as is everything else there.
 
Gonna have to go into the bios to see what Temp1 is. Tomorrow night. Working late tonight.
 

 
yep....converting that 85C to F is about 185 degrees F which is not good for the cpu.....basically, the cpu is overheating...
probably needs new thermal paste and just a little cleaning and loving and all should be fine.....
That's what the bios is suppose to do is if the cpu reaches a critical temp,  the system shuts itself down so it doesn't ruin the cpu.

But the system does not shut down. The video goes black. That's all that happens.

Maybe the heat is actually causing the GPU to shut down, not the CPU?

from the speedfan faqs:
 
There are several ways to label available readings (temperatures, voltages, fan speeds). The first source should be the BIOS. Enter BIOS at boot, write down labels and readings and compare them to those reported by SpeedFan. You can use manufacturer's custom hardware monitors to match readings too. SpeedFan strictly adheres to available datasheets for each sensor chip. Please remember that hardware monitors chips have some pins (small connectors) that should be connected to some additional hardware (temperature probes, thermistors or thermocouples) in order to be able to read temperatures. Only a few hardware monitor chips do label their connectors with "CPU", "System" and the like. Most of them use labels like "Temp1", "Local" or "Remote". Hardware manufacturers connect available pins to different temperature sensors basically according to the physical placement of components on the motherboard. This means that the same chip, an ITE IT8712F, for example, might be connected to a sensor diode measuring CPU temperature on Temp2 and, on a different hardware, it might be connected on Temp1. If you have a "Local" sensor and a "Remote" labeled one, this usually means that "Local" is the temperature of the monitor chip itself and "Remote" is the temperature read from a "remote" probe. When you have properly identified which temperature sensor is which, try to lower the speed of each fan and look at reported speed and temperatures. This way you can match PWM controls (speeds) with fans. Please, note that if you do not allow SpeedFan to change any fan speed and set all the speeds too low, then SpeedFan won't be able to avoid overheating.

bapu

JohanSebatianGremlin
Saying the fan is running doesn't tell the whole story. What does the heat sync look like? Is it completely clean or can you see dust on it? 

Clean.
 

JohanSebatianGremlin
If you spin the fan blades by hand with the machine off, do the blades spin freely without restriction? Or do they spin once or twice and then immediately stop?

Spins cleanly.
 

JohanSebatianGremlin
How about the rest of the innards, how do they look? Clean or dust bunnies everywhere?

Very clean, just a little dust.
 

JohanSebatianGremlin
Has anything else changed recently? For instance did they get a new computer desk with a little cabinet for the computer tower? Or as I like to call them, a computer desk with its own Betty Crocker Easy Bake Computer Oven.

Nope same desk, setup for the last 7 years or so.
 

JohanSebatianGremlin
Also don't rule out the monitor itself. 

Haven't yet.

Ok so looks like the fan and heat sync are good. That leaves the thermal paste as a possibility. I've never really seen thermal paste just break down from age, but I suppose anything is possible. 

Also leaves something else on the MB (possibly related to video) getting hot and going offline. The thing is, if the video signal from the computer was going offline, I would expect a no signal message on the monitor. That your screen is going black means either the video chip in the computer is failing/locking up in such a way that's actually painting black, or something internal to the monitor is giving up the ghost and shutting the screen down while still keeping the power LED green. Notice any unusually warm spots on the monitor itself?

Beagle
I REALLY hate to disagree with Jim, but I have seen this happen on two different systems.  both times the system would shut down without warning, just "go blank" after reaching a certain temperature and that didn't take long.
 
In both cases, the system would do exactly as you described.  the screen would go blank, the fans would all still be running, no beeps or anything from the computer.
 
...
 
both computers I removed the cpu fan, cleaned the thermal grease off of the cpu, replaced the fan with a new one using new thermal grease and everything worked like a charm.
 
...
 
 

I have a similar problem on one machine, but mostly is that one can not reboot/restart the machine as it might not come back up. All I gotta do is wait 5 minutes, reset the power supply and it comes up fine. 
 
The motherboard has no new drivers since the original, thus the BIOS can not be updated, and yeah ... that computer is about 5 to 6 years old, and it is pushing a GTX 760 ... and it's actually faster on WoW switching zones, than my SS machine with twice the memory and a faster video card (GTX 970).
 
This 2nd computer is only keeping back up copies and hard drive is not an issue. The same thing was happening before with W8 and W8.1 ... and I'll just take it a bit further and upgrade the motherboard in the next year or so.
 
My guess, and it is a GUESS, this is an issue with the motherboard, and it could be related to heat, however, it would be odd that it would heat up after so many hours, when most computers are designed to be able to stay on without overheating. I'm guessing that it won't get better either, and it might be time to swap out to a new motherboard?