Need help with computer related stuff!

[Bamtoman]

Here is the mystery I must solve :
While I was rebuilding my old computer, I put in a 9500gt into a pc that has a 420w power supply. The 9500gt only requires 300w or 350 w power supply. But when I try to turn on my pc, it just shuts down after 0.4 seconds. When I take off the 9500gt and just turn it on, the computer turns on successfully and stays on normally.
I used to use the 9500gt with a 500w power supply. But when I try to use it with a 420w power supply, my pc will just shut down in 0.4 seconds -.-"

Anyone got any solutions for my problem ?
Anything will be appreciated

Thanks

Oh btw the 420w power supply used to run my 9800gt but trying to run a 9500gt won't work ...

[BloodBane611]

This is a much more appropriate section.

Have you tried popping in the 9800 in as a test?

[Tim270]

Have you got any other gfx cards to test with? It could easily be a fault with the card rather than the PSU imo.

[whatshisname55]

He says he used to run the 9800 with his 420w. Are there any differences with other components since changing from 9800 to 9500?

[Bamtoman]

Ok, I tried running the 9500gt with a pc that has a 750w power supply and computer shuts down 0.4 seconds.
So I guess its the GPU that is too blame

Anyways thanks for the help, I will go sad face now...

[whatshisname55]

How long have you had it? Is it still under warranty?

[Darkpowder]

Put another friend's card in the slot to see if you have a slot/mobo problem. GPU failure can result in quick shutdowns, but often its a power-circuit related issue. If another card doesn't solve your issue you are looking at a mobo.
Don't forget though PSU's can degrade in the ammount of power they can supply if they are very old, so if you are on the borderline when you buy a PSU, in 5 years you can be a few % degraded.