no monitor signal

ok i dunno what the deal is.... the monitor isn't broken, works for other machines. the hard drive is recognized and i did back it up on another machine. the ram is fine in other machines. i can't get it to boot up. it sounds like the hard drive is spinning and trying to boot up but there is no signal to the monitor. i tried to reformat in a different machine but was unable to (does the same thing with the disk in the messed up machine as if it wasn't there). the processor does not appear fried and i never noticed smoke or smell from it. the last time i tried to reboot it, i changed the startup options using msconfig. i switched so only neccessary windows files would startup during bootup. but it never came back. i thought that was just a coincidence. i dunno what the deal is. any help would be greatly appreciated.