When I start the system up it works fine but when I went to update the Windows Vista index rating and it tried to test the GPU the system shuts down unexpectedly this also happens when I load a game up, what could cause this to happen?
If you want to get a PSU not on the list, you take on a little risk by figuring it out yourself and hoping you didn't miss something. You need enough amps added together to power two cards plus the rest of your system. If your card's docs say exactly how much watts and amps it draws, it's easy -- just double plus add the amount for the rest of your system. If they explain the total needed for system + 1 GPU, you can double it but then you need to figure out how much of that was for the system and subtract it out so it isn't counted twice.
Example, I have 2x 8800 GTS 512 SLI with a PSU that is 650W and 22A + 24A on the two rails. The GPU manufacturer recommends 425W 28A for one card. If I double that, I get 850W 56A ... that is more than my system has yet I know my system's OK. So being conservative I can subtract that difference and guess that's what my system needs in any future calculation ... which is 200W 10A.
So for instance if I was building 2x GTX 260 SLI which needs 525W 38A for one card, I can double that and subtract 200W 10A and figure that is what my system will need with the two new cards ... that is, I need to shop for an 850W 66A PSU solution.
Of course there's some uncertainty there, and I might lose some money or blow a component if I'm not careful ... but that's part of the fun for me.
What i think I have it narrowed down to is that the 9800 GT 's have a max pull of 26A. My PSU has two 18A connections.
I'm about to order a new power supply, what I'm not sure of is that if the connections are single rail do I need a minimum rating of 52A to power the cards. Or would a rating over 26A be sufficent.
Tom's did an article on power consumption, and it turns out your 9800 GTs (aka 8800 GTs) consume about 10 amps each at max load. That's all. Card manufacturers grossly over exaggerate the requirements
Nevertheless, your PSU still sounds like it's the culprit. Not because it's too weak though, but because it's just flat out not working right. Inconsistent power (such as power dips/spikes) can cause crashes in the same way that a weak PSU can. A new, high quality PSU would probably solve your issues, but you don't explicitly need a much stronger one.
Though it might be a good idea to get something stronger if you plan future upgrades