|State the make and model of your brand name system, or if it is a generic system, the make and model of the desktop mboard. |
The specific brand name system model is usually on a label on the outside of the case somewhere, or it can be determined by going to the brand name's web site.The model of the mboard in a generic system is usually printed in obvious larger characters on the surface of the mboard, often between the card slots.
If you have a generic desktop system, or you can do this in any case.....
Unplug the case/power supply.
Power off your monitor.
Open up the case by removing the left panel as seen when you're looking at the front of the case.
Find the label on the power supply and the maximum total output rating - tell us what that is.
Your power supply may not have enough capacity.
The 8400GS chipset requires the power supply on the system has a minimum 350 watts output capacity.
(Minimum recommended power supply with +12 Volt current rating of 18 Amps.)
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!)
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 more than one +12v amperage rating - they have two or more - in that case you add the rated max amperages to determine the total +12v amperage rating.
A video card that requires more PS capacity than you system has often works for a while anyway, but the PS is overloaded 100% of the time and is eventually damaged and fails.
If you need a power supply 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: