This is a common issue for cpu bent pins, can you take close up clear images of your cpu socket to check there are no damaged pins?
You have a second gen i5 so you'll have intel hd 3000 graphics, so take out your gpu as you don't need it to boot, take out things like dvd drive and leave only one stick of ram too.
I see Gloup has suggested to flash the bios but obviously you can't do that yet if you can't boot.
I'd suggest removing the motherboard from the case, putting it on the box the motherboard came in (or any cardboard box), and install only the necessary items onto the mobo to get it booting, if it works it could be the case shorting the board, check all connectors are correctly in place too!
Get back to us with more info and the pics i've requested