Hooo Boy, you're probably on the right course, with it being the power supply. Does anything else light up or power on, the CD?
If not, is this a notebook or a desktop? If a notebook, best to contact the manufacturer. Too many ifs and too many things to goof up inside plus just not enough information.
If its a desktop, do you have a multimeter or even just a voltage probe? Something that will register down to 1 volt. If so,
1) open it up and check all the power connections. Since its not even trying to boot, that means power isn't getting to anything.
1)a - First of all check the power supply and make sure all the connections are good. If that doesn't solve the problem,
1)b - then check to see if the various leads coming out of it are producing power, using the multimeter or probe.
1)c - If they are good, then reconnect them all and make sure the connections are solid. I'd say to check the fuse but the mouse is getting power so that's not likely it.
2) If all the leads out of the power supply are tight and have power, make sure all your components are seated well. Before you touch anything make sure you are grounded out by touching the case where there's metal. No point in frying something before you figure out what's wrong, one problem at a time is more than enough. If everything is seated well, its getting past a minor problem.
3) Check for funny smells or indications of something burnt. Past that, you have something serious wrong. Something like the CPU is dead. I mean, if nothing fires and there's power to everything, its got to be the CPU is dead. Or the BIOS are chucked, maybe the board battery is dead, I don't know if that will stop it from starting up though, it just wouldn't go into POST, but I'm pretty sure the drives and fans would fire up.
Good luck, hope its something minor, just a loose connection. Let us know.