@renatocoel46366 let us know what the issue was that prompted you to check your display cable. first try to reset your RAM. Remove it from the slots and then reseat the module(s) again.
Next try this
Turn off the computer. If you are unsure whether the computer is off or on, turn the computer on, and then shut it down. Yours does not come on so this should not be an issue but we just have to stay consistent.
Disconnect the power from the computer by unplugging the power cord from your computer.
Disconnect all external devices from the computer.
Remove the battery
Now hold the power button depressed for about 30sec-1min.
REapply the AC power adapter and see if your computer does now show any sign of life.
Since this happened after you (sort off) took it apart, double check all the connectors. Make sure that everything is seated properly. I know you said your power supply is good, but you want to check your power supply anyway. Make sure it has the proper voltages. Check the DC-in jack of your laptop. Make sure there is no corrosion, debris etc. that prevents it from working. After that you need to check and see if your motherboard even gets power. For that of course, you need to open it up.
Fir any further and deeper help, we would need to know your exact motherboard number. It should be printred on the motehrboard. To work on your compurter use the Maintenance adn Service guide [http://h10032.www1.hp.com/ctg/Manual/c06219881.pdf|from here]
If you are stuck or see anything that requires some sort of explanation, post some pictures of that with ypour Question [guide|21499]