|You are overloading your power supply!!!|
It WILL fail eventually when you have this video card installed!
You need one with more capacity!
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.
For Radeon X1950 Pro AGP, this is typical:
Visiontek Radeon X1950 Pro / 256MB GDDR3 / AGP 8x / DL Dual DVI / HDTV / Video Card
"450 Watt power supply or greater recommended" !!!
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: