|Who told you what, and where? This is your first day and first posting here. You might want to explain what you've done already and what if anything happened to it between the last time it worked OK and the first time it didn't.|
Hold on, I have to eat this yoghurt before it goes bad.
(a few minutes later)
OK, do you get any beeps when you start it up?
A power supply can be working enough for fans and drives to spin up and LEDs to flash but that doesn't necessarily mean it's good. It has to provide other voltages at sufficient current in order for the motherboard to work.
Or the motherboard or something connected to it could be bad. So it's a good idea to temporarily disconnect all the drives and remove any add-on cards. Don't remove the memory. Do all this with the power cord disconnected as most power supplies provide a small charge to the motherboard even when they're off. Then plug the cord back in and start it up and see what happens.
That's just some basic stuff. We eagerly await your posting back with additional details and history.
message edited by DAVEINCAPS