How much experience do you have troubleshooting a system? If you don't have any, I would simply turn off the system and unplug the power supply. Remove the motherboard battery for one minute, and reinstall. This will reset the bios and might get you a post screen or some beep codes if your board has a built in speaker. If you don't care about the money you've spent, then you can learn how to troubleshoot by removing or disconnecting components until it posts if you're lucky. I would normally suspect the power supply or motherboard, but it could be something else, like a bad hardrive. Start by disonnecting the hardrive connectors, and try posting. Also check youtube or google for troubleshooting videos. They're out there; plenty to choose from.
Alright, I have a friend who's a bit more knowlegable coming over and hopefully he can help with this, as I have almost no clue about any of this..