I suddenly have no video display, monitor is fine, changed video card didn't work, new motherboard( bought same board) didn't work and different hard drive and Ram and still no display. When I turn computer on no beeps and all fans work, power supply lignt is on (grn) but no lights on front of tower and no caps light on keyboard. Could it be processor?

Yes.

Could you tell more about what you have? The no beeps is a tell tale sign. You don't need video card, RAM or drives to get beeps. Reduce the parts until it beeps or not. If you get down to speaker, motherboard, CPU and PSU with no beeps (notice no case?) then it's one of those parts.

The power supply (PSU) is a good candidate.

Hp 1534 Envy, it has a green light on power supply should mean it's working. Everything powers on but no display on monitor or lights on front of tower. It never had any issues or blue screened just was blank when I got home and turned on.

The green light only means the power to the green light and the light is working. If you want to dig in, get out a Volt meter and measure each leg.

On some PCs when the CMOS battery is too low, no boot so be sure to measure that at the same time.

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