The busy light being constant-on could be a continual reset state. Hard to tell without a POST Probe. Make sure your power button isn't just stuck in or broke in some way! And reset button too for that matter.
If it isn't just a stuck button then it could be a short on the bus. Try pulling out any cards you have in there, PCI/ISA, whatever. But not video if needed. Be sure to pull out cards/wires/jumpers/RAM etc... when the power is completely OFF. If the power button doesn't to it, pull the plug. Make sure that button is good! Then pull the cards and try again.
If pulling cards doesn't work, unplug any other cables to the board and try it with bare essentials: mobo/PS/CPU/RAM/Video and nothing else. With the BIOS having been freshly reset. If it still doesn't work it is one of those that is the problem. Likely mobo or CPU because you don't get a beep code. But even though the fans are spinning it could also be the power supply, bad 3v or some such. Have a local shop test the PS, they should be able to do it quickly and for free with a tester if they have one.
Good luck!