In addition to the other idea about trying a different power supply (pro tip: PC nerds should always have a known good power supply lying around on a shelf somewhere, for situations like this), also try yanking out and reseating your graphics card. If neither of the above do it, try sticking in a known good graphics card. Also check the power socket(s) on your graphics card for signs of having become cooked.

In addition to the Shelf O' Power Supplies, I also keep a couple of rinky-dink and/or several generations old graphics cards in a box (I even still have a couple of AGP ones!) because they're not worth anything but definitely do at least kick out a video signal, which is useful for troubleshooting a potentially bad card and also keeping you going — albeit maybe only in Flatland — while you wait for warranty or a replacement to show up in the mail.

The motherboard is telling you; it's unhappy with the graphics card. (VGA = Video Graphics Array) Try reseating it and its power connectors. If that doesn't fix it, ideally you should try plugging in a different card, if you have one.

Do you have a second power supply you can try?