This problem will occur in a running Desktop PC. The display will go off and you will get a message of “No Signal”.
Now as you switch on the UPS and just prior to power on of a PC, the monitor displays this message. This is because the CPU has still not booted and hence is sending no signal to the monitor. So if the same message is now visible after the PC has been running for some time, there are two possibilities.
Display goes off after the settings for turning off display have been set to a particular time. Or the PC is going to sleep mode. Once you are assured that none of these settings have kicked in then you are faced with a problem. This problem will be a recurring one, as I have experienced. The keyboard and mouse becomes unresponsive. So you can’t use the ctrl-alt-del option too. And you are forced to use the hardware reset button. All this while, the fans of processor and cabinet keep humming away to glory suggesting that the PC is still on.
Before we move on to the solution, a quick look at the inside of a Desktop PC.
The motherboard is a platform where components are connected. The SMPS powers the whole thing. A graphics chip is responsible for displaying whatever is the output of your PC. The graphics chip is either embedded on the motherboard itself in which case it is called Integrated Graphics Card. These are the usual run of the mill Desktop PCs for day to day tasks.
In other cases, the graphics is handled by a dedicated circuit, called a graphics card, mostly used for specific roles such as gaming, animation, design, video editing, etc.
The problem mostly happens on a Desktop PC with an Integrated Graphics Card/Chip. Chip itself going bad can be ruled out, since you PC does boot in the beginning and runs for some time before display going off. Two components are suspect here, the SMPS and the RAM.
The issue with RAM or the memory chip is that it rents out part of the memory space to the Integrated Graphics, so any issues with RAM will lead to display problems. In fact for a budget PC or assembled PC, it is recommended, to always invest in a branded and good quality RAM chip for a long and trouble free PC running.
Which leaves us with the last option, SMPS, again the most vulnerable component in a budget PC. SMPS, also known as Switch Mode Power Supply is supposed to provide stable power at the advertised ratings. But low cost SMPS never reach the mark. Good quality SMPS cost a bomb. Also the components in an SMPS keep deteriorating over a period of use or due to weather conditions like humidity.
When the PC boots, the SMPS is able to provide sufficient power to the components. But as PC starts running, the components get heated up, workload on the hard disk or processor increases, the SMPS cant keep up with the power demands and it starts compensating. The CPU or the hard disk can’t be shut down, so it looks for the next vulnerable option.
A replacement for the SMPS should be able to do the trick to solve the problem.