No Signal means no video signal from the computer.
Means the computer isn't sending a video signal to the monitor.
Logic would dictate that the problem is the graphics chipset.
Whether it be Integrated Graphics (OnBoard) of the motherboard, or a separate graphics card.
However there is a different culprit, and one that is often overlooked,
A Power Supply with a weak voltage power rail, will not have enough power to turn the Processor (CPU) on.
1) If ALL of the LED lights were on at once, they would use less than 1 Watt of power.
2) EACH fan uses 2 to 3 Watts of power
3) A typical Processor can use 51 to 125 Watts of power,
Just depends on what Processor it is.
This is why one may see LED's light, and possibly fans spin, but No Signal.
Not enough power to turn the Processor on.
Computer dirty inside? That just 'kills' a Power Supply.
The cooling components for a Power Supply, is the Heatsinks used inside, and a small internal fan,http://en.wikipedia.org/wiki/Switched-mode_power_supply
Click on the photo of the exposed Power Supply, to enlarge.
Looking in-between the letters B and C, plus C and D, you see Heatsinks.
Fins arranged in block shapes, and attached to a single piece of long metal.
The Heatsinks absorb heat from whatever object they are placed against.
The thin fins of the Heatsink then radiate the heat away.
Air flow from the small internal fan, helps carry heat away from the fins of the Heatsink's.
When dirt, dust, hair, carpet deodorizer, lint,.....you name it; coats the fins of the Heatsinks, and the blades of the fan, the Power Supply overheats.
Heat = Wasted Energy
The Power Supply tries to keep up with the call for power, but eventually components inside fail, (Go bad), and the Power Supply fails.
Number one thing when diagnosing a desktop computer, is to make sure the Power Supply is good. Make sure it is putting out the correct voltages.
Power Supply is deemed to be good, THEN go on.
Next thing in the list for desktop computer failure, is the computer is dirty inside.
The Power Supply in your personal computer (PC), is an Converter.
It converts the high AC electricity from your home, or business;
(120 to 240 Volts AC, depending on country), into 3 low DC Voltages,
A) 3.3 Volts
B) 5 Volts
C) 12 Volts (ALL are DC Voltage)
In comparison two D cell flashlight batteries produce 3 Volts DC.
ALL Orange wires are 3.3 Volts
ALL Red wires are 5 Volts
ALL Yellow wires are 12 Volts
ALL Black wires are Ground wires.
A multimeter set to DC Voltage, is used to check those power rails.
Use a KNOWN to be good, Compatible power supply, for a temporary test unit.
Power is known to be good now?
Then I concur the Integrated Graphics on the motherboard may be bad.
Use a graphics card.
Using a graphics card bypasses the motherboard Integrated Graphics. Attach the monitor to the graphics card.
FOLLOW Anti-Static Procedures.
Graphics card is installed. Monitor hooked up to it. Turn the computer on.
You should get a display, albeit it is going to be a 'Fred Flintstones' looking screen.
Screen resolution won't be correct, and Color quality will probably be 8-bit.
Looks worse than a computer using Windows 95.
That's OK. You can now install the Drivers for the graphics card, because you can now at least SEE the screen.
Post back in a Comment.
Want to know about Power Supply first.