Computer Boot Problem?

Hi, hopefully someone can help me here so I don’t have to waste money buying the wrong components.

I have a HP desktop that won’t boot. It starts for a second or two then cuts out. It have no display, I have tried a different graphics card but that makes no difference either. Sometimes the boot will last a second sometimes it stays on but no display. The hdd spins up, the CD drive spins but the computer won’t stay on.

I have posted a YouTube video of this happening so you can see for yourself

Any help would be really appreciated

Regards,
Sam.