|It sounds like either your power supply has a poor connection, or the power supply is in the beginning of the process of failing. |
You could try this...
Unplug the case/power supply, or switch off the AC power to it otherwise.
Power off your monitor.
Unplug the main connector from the power supply to the mboard, plug it back in.
The wires close to the mboard going into the main power connector/socket should be more or less perpendicular to the mboard surface rather than at an angle. Make sure all cards in slots are all the way down in their slots.
There is probably a smaller connector from the power supply that plugs into a smaller socket on the mboard - unplug it, plug it back in.
Make sure that the connector for the power switch is no loose on the pins for that on the mboard - see your mboard manual if you need to.
Restore the AC power to the computer and try it.
If that doesn't help, I suspect the power supply is in the beginning of the process of failing.
Failing power supplies are common and can cause your symptoms.
E.g. They often will not boot the mboard properly intermittently in the beginning stages of failing.
Check your PS.
See response 4 in this:
If it is failing, you can usually replace it with any decent standard sized standard ATX PS with the same capacity or greater.
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:
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.