What is your CPU, motherboard, graphics card model make, model number, etc. Does the CPU model have graphics capabilities?
First disconnect everything, including hard drive and DVD drive, except for RAM the power supply. Any peripheral that is shorted or is not connected correctly can effect the entire system
Does the system turn on and stay on? If nothing could be the power supply itself.
Or "No" then turn off with power switch and reseat RAM modules seperately and try again.
If yes then add the graphics card. Does it work? If yes then good if no defective graphics card.
Just add one item at a time until faulty device is discovered.
A PC motherboard speaker will "beep" to give error codes which you can look up for your motherboard/BIOS version.
https://www.youtube.com/watch?v=aCCFlC_tlcI
There's a start. Let us know how it goes.