Dell Dimension 3000
It would not boot to the system, HD, CD/DVD.
Would not activate the display and so I cannot see the BIOS startup (F4, F8 keys etc) screen, so
I removed/replaced the Ram
I removed the PCI cards
I disconnected the HD
I disconnected the HD, CD
I disconnected the HD, CD, Floppy I have replace the logic board with a New one and repeated all the above steps
It gets full power fine and does power all the above bits of hardware fine, + fan, lights...
There are no lights on, you know, the 4 lights at the rear of the Dell PC, so that’s a good thing?...
Just because the fans spin up does not mean it is powering up everything fine. Still could be PSU, CPU, RAM, or the onboard memory controller not accepting the RAM for sharing with the video. Also, try 1 RAM stick at a time and listen for beeps when it is powered up.
Do you have another PSU to borrow from another rig to test it out? That can rule out the PSU issue now.