So, if your PC is old or new and it does not boot or has no display then what do you do?
-During connecting or disconnecting devices, be sure to have the AC electrical power disconnected
-Temporarily ground yourself, or use a wrist strap to prevent electric static discharges from destroying certain components.
Here are my troubleshooting procedures:
-With a new motherboard: verify if all mounting standoffs' holes correspond with the holes in the motherboard!!
Or test the motherboard outside the case, on a wooden (non conductive) surface
-Clean the system from dust, then test with the minimum setup:
- Disconnect all peripherals devices (including the drives, CD, DVD, printers and keyboard) and network cables, except for the motherboard + CPU + 1 ram stick, video card, monitor and power supply
-Verify that the 4-, 6- or 8-pin CPU Aux power plug is connected
-Verify that the VIDEO card has a power connecter - if yes, connect the power to it!
Now, power-on your PC. On boot, do you have a display?
-if NO it is one of the connected devices: RAM, Power supply , video card or monitor. So, if possible, swap ram, power supply, video card or monitor - leaving only motherboard and CPU
-test the ram in each slot, sometimes you have abad slot, causing ram problems
-if YES, then disconnect the AC electrical power, and start reconnecting each of the peripherals, devices and cables (one at a time) until the problem shows itself. Before each of these reconnections, you need to follow the precautions above.
*** note : if the fans are running, this shows there is 12 V present from the power supply; this does not mean the power supply is ok, you still need 3.3 V and +5 V as well; and other signals.
Additional tests and things to try :
-boot without ram, it should beep; (also, without video card)
-try the bios default settings, (if possible) or clear the bios by removing AC and the bios battery
-renew the CPU heat paste, and verify that the heat sink is mounted flat on the CPU, allowing for a good thermal contact
-you can also check the motherboard for bad capacitors as shown here :
- test parts on another PC to know what is ok - and what not - if possible
***note : if you are using 4 sticks - note that many boards do not run well with the ram bus loaded heavily like that, causing deterioration of signal levels and wave forms ! --> so test with 2 sticks max ..
The term POST refers to the Power On Self Test procedure - here a link with a short explanation