07myonyunt, I've looked at all three problems you've posted.
Here's a list of what I would like you to check, and post your diagnosis back to me in a Comment.
1) As mentioned in a previous solution, check the cables inside your computer to make sure they are connected well, you have all the necessary cables hooked up, and to include the power cables coming from the Power Supply.
The Asus PK5PL-AM SE, and the PK5PL-AM/PS, use an LGA 775 processor socket for an Intel processor. They also have to have a 4-pin ATX +12 Volt power cable connected to the motherboard.
Example of a 4-pin ATX +12 Volt power cable.http://www.playtool.com/pages/psuconnectors/connectors.html#atx12v4
It's power for the Processor.
PK5PL-AM/PL motherboard. Click on the Specifications tab.http://www.asus.com/product.aspx?P_ID=y014Wy067iZxxPeP&templete=2
PK5PL-AM SE motherboard. Top View - 4-pin ATX Power Connector,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4496442&CatId=3461
Hooked up, and attached tightly?
1A) How about the 24-pin ATX main power cable?
1B) 15-pin Sata power cable attached to the Harddrive, as well as the 7-pin Data cable?
2) Are the Ram Memory modules seated tightly?
If you are using just one Ram Memory module ('Stick') it has to be in Slot 1.
The Ram Memory slot that is closest to the Processor.
(DDR2 Sdram at either 667MHz, or 800MHz. PC2-5300 and PC2-6400 respectively)
If this was a running computer, and has some age on it, you might want to remove the Ram Memory module/s, and clean the gold plated contact pins on the bottom. Corrosion can develop on the contact pins. Doesn't take very much to make a bad contact. (It won't be discernible with the human eye)
Follow Anti-Static Precautions after you have unplugged the computer from power, and use a pencil eraser to clean the contacts of the Ram Memory module/s. Use air to clean off the eraser dust before reinstalling.
(If you have a can of compressed air for computers available, use it. If not air pressure from your mouth will be sufficient)
If this is a computer build, did you follow Anti-Static Precautions when building it, or while working on it?
Before you took the parts out of their anti-static bags/boxes, and during building?
3) If everything denotes a Yes, then I suggest you have a bad Power Supply.
Weak voltage power rail.
A) ALL of the LED lights in use at one time use less than 1 Watt of power.
B) EACH fan uses 2 to 3 Watts of power.
C) A typical Processor can use 51 to 125 Watts. Depends on what Processor it is.
Enough power to light LED lights, maybe spin fans, (Or spin a few times then stop), spin the Power Supply fan, but Not enough power to turn the Processor on.
No Processor operating, no finding the Boot record on the Harddrive. Essentially a non-working computer.
(No computer operating No Video Signal is produced to the monitor. No Signal)
Do you have a KNOWN to be good, Compatible power supply for a test unit?
Perhaps in an unused computer.
Perhaps someone has upgraded computers, and has an unused computer with the Power Supply you need for a test.