Well, you commented about not sending signals which leads me to believe it is booting properly. But first verify it is properly booting: Turn it on and listen very closely for hard drive activity, it will sound like clicking. The cd-rom should also blink a few times and eject when you press the button. If it does you probably blew out your GPU (not uncommon) an easy fix is to buy a PCI VGA adaptor.
Disconnect all wires, Put your left hand on the power supply, and plug the PCI card into the PCB board. Once you reboot that VGA port will work in a mirrored mode. As an end-user, it works. As a professional, one should disable or remove the old adaptor.
If you do not hear clicking, it is time to throw down 300$ for a new PC or splurge for the Mac.
** I am a certified professional, check my site, personal site, if you know it **