Gamja, it only takes about three to five seconds to fry the cpu without a heatsink and fan. Don't try to boot it up to see if it works, it'll fry before you see the startup screen.
Money_man-No offense-he said he connected the cpu fan connector to the chassis fan connector. That will not work as the mobo senses the cpu fan operation from the cpu connector and will not allow a boot without the proper input from it.
It really sounds like your graphics card. Does your hard drive come on? And if the hard drive is working, try something else. if your mobo has integrated graphics, take the monitor pug out of teh graphics card and plug it into the mobo.