I would start by checking the cables and making sure they're tight and secure, after that check your fans to make sure nothing is stopping them and then I'd check your power supply with a multimeter to verify correct voltages are being supplied. If correct voltages are being supplied, cables are tight and still nothing upon powering on you may have a faulty graphics card in need of repair or replacement or a bad monitor.
How do you know the mouse and keyboard are working if you cannot get anything to display on screen? It sounds to me like you have a bad graphics card or maybe a bad input on your monitor. Are you using the same input and cable for your ps4 as for your pc to make absolutely sure you can rule out the monitor and cable as bad? Also when you power up your pc do you hear any beeping coming from inside the case? Assuming that your internal speaker is connected your motherboard will indicate to you any errors with booting when first powering on. Also if your motherboard offers on board graphics as well as having a pci or pci express graphics card the settings may be expecting a monitor on a different output than the one your monitor is connected to. We're you able to verify that your power supply is supplying the correct voltages with a multimeter?
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