Hi molavydez,
It could be a core component that has gone but the only way to be sure is to rule out all the other components.
Heres what I suggest(excuse the length)
Disconnect everything from the main box & open it up.
Disconnect the power & other cables from the DVD & hard drive as it might be as simple as the DVD drive shorting out.
If that doesn't work then another test you can do is remove the memory and switch the computer on. If the computer emits three long beeps then your processor & motherboard is most likely fine.
Plug one of the memory sticks back in & Reset the "CMOS switch" on your motherboard(you might need to google this one if you don't know what I'm talking about - google images should help you)

you probably changed the resolution of the monitor wit the monitor ooption instead of the Desktop Display setting. If possible, change it back to 1024 x 768 or 800 x 600.

Also, if the video card has a TV Out, attach a cable to it and to TV. This happens quite often when your video is "cloned" and you don't set the Primary display to Monitor. The Nview (Nvidia) Display Master Control sometime acts on its own and changes the Primary Display to TV. Disable Nview from Taskbar.

when you power on your machine, have you tried pressing some keys on your keyboard, like caps lock or num lock and check whether it's responding or not. if it is responding then do as Jupiter 2 suggested. it could be display settings only.