Is it getting power? Is the power supply "surging"? (I think I might've made up my own word) The only reason I ask is that happened to me once. New computer, new power supply. Hook everything up. Power on the power supply. It was bad. Sent a surge through all my hardware upon first turning it on. Fried everything.
I would say that if your Keyboard lights do not blink, no beeping and no post it may be that the Hard Drive cable is either not plugged in completly or a jumper setting on the motherboard is set to the wrong IDE slot for post. I would reccomend to check the motherboard for the IDE or SATA connector. Try reseating it (uplug and replug) If it still fails it may be a possible jumper setting on Motherboard to set to correct bootup IDE or SATA Startup.
try to boot up your computer without the data cables, connected to the motherboard, so you can isolate other problems...then power on your computer check if the keyboard led's flash, checked also if the cpu fan rotates..then if the keyboard led's didn't flash and cpu fan doesn't rotates , then try to double check all your jumper settings..
You might also need to replace your CMOS Battery as well. Make sure it is seated well on the motherboard. If you CMOS battery is not installed correctly or it needs to be replaced the system will not boot at all. No fans, no power (sometimes you see limited power such as a dimmed hdd light.)