FYI nighthawk computers require the monitor device be active and ready to accept signal when you power it on, otherwise it will not output video. some TV's take a while to become ready... necessitating the use of a delay relay to postpone the computer booting for a few seconds while the TV boots up.
that said, if you aren't getting video, it sounds like an issue with the computer. the IO board will provide no information regarding your computer besides the fact it's being powered and connected.
gonna have to peel it open and have a peek inside the computer box. look at the motherboard and the video card for swollen caps with the top pushed up or the bottoms blown out.
reseat the video card/ram sometimes these get yuck on the edge connectors. (it seems the video cards are especially prone to this) run a pencil eraser over them and then wipe with isopropyl alcohol. (ideally 99% if you can get it)
check your CPU cooler and see if it is the thermaltake LGA755 type with the long plastic area where the screws go in. the bottoms of those bust out leaving no pressure on the CPU and it overheats and dies. grab your cooler and give it a gentle little wiggle and see if it's firm. if it's wiggles and feels loose, you have busted mounts. replace it with a cooler with an all metal bracket. if it's firm, leave it... but keep an eye on it. it can bust on you at any time.
if your cooler mounts are busted, your CPU could be toast.
i've had to clear the CMOS of some of these boards to get them to boot up again. not sure what causes it. maybe glitched or corrupted CMOS settings. maybe a protection thing from overvoltage or over temp... probably a good idea to swap the battery in it anyway.
possible failing power supply. i think 1 out of every 10 i have to fix has a power supply that tests okay at the low load of a power supply tester, but fails under load. if you have one you can swap in to just test that would eliminate that as a potential issue.