|Did you unplug the cord to the case, or otherwise switch off the AC power to the case, at ALL times when you were plugging in or unplugging anything that plugs into the mboard ? If you didn't do that when you were plugging in or unplugging the video card, you may have damaged the video card !|
What is the specific model of your mboard ?
Some fairly recent and new mboards that have onboard video have a Hybrid video feature - both the onboard video and certain video chipsets on a video card will be enabled at the same time by default when you install a video card in a PCI-E X16 slot.
If you install a video card in a mboard slot that has a video chipset that is NOT compatible with that feature, you will NOT get video from the video card by default, and the onboard video is still producing video.
In that case, you need to change some settings in the bios - we need to know the specific mboard you have in order to be able to tell you what you need to change.
Some AMD and NVidia main chipset mboards have the Hybrid video feature, in which case Hybrid Crossfire or Hybrid SLI is always mentioned in it's specs, and some Intel main chipsets also have that feature - they call it something else - Hybrid Multi-monitor Support.
If you mboard does not have onboard video, or if it does but the mboard does not have that Hybrid video feature, then there is NO setting you can change in the bios that disables the onboard video - that's done automatically by the bios when you install a video card in a PCI-E X16 slot (if the card is not damaged, is hooked up correctly, and is all the way down in it's slot).
If the onboard video adapter shows up in Device Manager, then the mboards bios hasn't disabled it.
The fact that it shows up there indicates you have a mboard with the Hybrid video feature, and/or the mboard is not detecting the video card at all, for whatever reason.
It doesn't work to un-install the onboard video adapter in Device Manager if it shows up there - you must Disable it, otherwise it is just detected again the next time you boot the computer.
If the video card has one or two power sockets on it, you must connect a wiring connector from the power supply to that (those) socket(s) that fills the socket(s).
If your power supply does not have the necessary connector(s) on it's wiring, if the video card did not come with (a) suitable wiring / connector adapter(s), you must buy (a) suitable wiring /connector adapter(s) and connect it(them) to the power supply and the card.
Your power supply must have at least the minimum capacity required to support a system with the graphics card you are using installed, or the max graphics card you might install in the future.
(Onboard video - video built into the mboard - IS NOT A CARD ! )
If that info is not in the ad for the video card, you can go to the video card maker's web site and look up the specs for the model - often under system requirements - the minimum PS wattage, and, more important, the minimum amperage the PS must supply at 12v is stated. If you don't find that, any card with the same video chipset including any letters after the model number has very similar minimum PS requirements. Some power supplies have two or more +12v ratings - in that case, add those ratings to determine the total +12v current capacity.
If you're a gamer...
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It's recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should get.
If you need to get a PS with more capacity, you can usually replace it with any decent standard sized standard ATX PS.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.
Don't buy an el-cheapo PS.
See response 3 in this: