That's because you have a Power Supply with a weak voltage power rail
How do I know this?
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.
Your motherboard? http://www.intel.com/content/www/us/en/desktops/desktop-board-dh61ww-classic-brief.html
With the LGA 1155 processor socket, and the Intel H61 Express chipset, it can support Intel Core i5, and Core i7 processors.
(That use an LGA1155 processor socket)
Information on the Intel H61 Express chipset,http://en.wikipedia.org/wiki/List_of_intel_chipsets#Core_i_Series_chipsets
List of Intel Core i5 processors, that use the LGA1155 processor socket,http://en.wikipedia.org/wiki/List_of_Intel_Core_i5_microprocessors#.22Sandy_Bridge.22_.28dual-core.2C_32_nm.29
95 Watts maximum (TDP) Also scroll down.
List of Intel Core i7 processors, that use the LGA1155 processor socket,http://en.wikipedia.org/wiki/List_of_Intel_Core_i7_microprocessors#Sandy_Bridge_microarchitecture
95 Watts M-A-X-I-M-U-M. (TDP = Thermal Design Point) Also scroll down.
What is happening?
You press the Power On button. This plastic button in turn, presses against the Power On switch. A Momentary Contact Switch.
The brief closing of the Power On switch, closes the Soft Power On circuit, in the Power Supply.
The Power Supply turns on.
The first chipset to receive power is the BIOS chipset. The BIOS program starts.
BIOS looks to see what devices are connected, does a Ram Memory count, TURNS the Processor on, and hands the computer over to the Operating System.
(Windows XP, and Windows 7, are two examples of an O/S)
When BIOS goes to turn the Processor on, the Power Supply 'falls flat on it's face'.
Has to enough power to light a few little LED lights, and maybe spin a fan, or two, but NOT enough power for the Processor.
The monitor is stating No Signal, because there is no video signal coming from the computer. This is because the computer is not working, because of that bad Power Supply.
[Weak voltage power rail ]
Want to know how to test the Power Supply?
Post back in a Comment.