Help Please!! Computer turns on but does not start up

[casualpanda]

Hello, i built my own computer not long ago and it worked perfectly, but recently it has been starting up but not completely turning on. What I mean is that it turns on but does not do any beeps and the monitor does not turn on. I can hear and see everything else turn on but the monitor will not go on and the system will not beep. I have replaced my video card, mother board and powersupply and it still did it but sometimes it would turn on for some reason. Now it won't start up at all anymore since today. My power supply can plug into my hard drive with a SATA plug and/or an HDD and the hard drive is connected to the mother board with a Serial ATA connector. Anyone have any help on how to fix this problem??