Monitor has no signal

[JunPAHA]

Two weeks ago, when I turned on my desktop computer, there was no signal on the monitor. I have done many things but could not solve the problem. Here are what I have done:

1. Used another connection cable (HDMI) for connection, in addition to VGA.

2. Connected the computer to another monitor and tried both HDMI and VGA. I set the connection mode to HDMI or VGA for the specific cable that connected the computer and monitor.

3. connected the computer to a TV using HDMI.

4. Took out the video/graphic card and put it back.

5. Replaced the old video/graphic card with a new one sent from HP.

6. Reset CMOS by replacing the 2032 button battery with a new one and reset the CMOS jumper on the motherboard.

7. Removed all three memory RAM cards and put them back to make sure they were not loose.

8. I also tried only one RAM card each time when I tested the computer.

9. Bought a new power supply unit and replaced the old power supply.

With all the above efforts, the monitor still has no signal. One thing I did observe was, occasionally, a few seconds after I pressed the power button and the computer started to run, the computer suddenly shut down everything including lights and fans just like no power. A few seconds later, the computer gained power again by itself and started to run. This did not happen every time I turned on the computer but did happen occasionally.

Does anyone know any possible issues with my computer? Thanks so much for your help and suggestions. 

[Prométhée]

Hello
If this is possible with your computer, have you tried removing the graphics card, and connecting the monitor to the motherboard ??
if it is the same, according to what you indicate, it is very likely that the motherboard is defective

[JunPAHA]

I haven't done it. Do you know how to connect the monitor to the motherboard? Thank you for your suggestions!

[Prométhée · Accepted solution]

is it this one ?

 HP ENVY h8-1520t Product Specifications and Configurable Options

if yes

 Motherboard Specifications, IPMMB-FM (Formosa)

Intel Graphics Media Accelerator HD Integrated graphics (DX11)

*Integrated video is not available if a graphics card or an Intel processor ending with “P” is installed.

• Integrated graphics depends on the installed processor:
  • For Sandy Bridge processors: Intel HD 2000 Graphics or Intel HD 3000 Graphics
  • For Ivy Bridge processors: Intel HD 2500 or Intel HD 4000 Graphics
• One PCI Express x16 slot (Gen 3.0)

5  DVI-I: 1 and DVI-D: 1

[JunPAHA]

Yes, that is correct. I just ordered one from ebay and hopefully it will work. Thanks so much for your help!

[Prométhée]