Gateway GT5435E MCP61-P AM2 Q's

I have 2 gateway pc's and the motherboards are the same model ECS MCP61-P AM2 and in one of them I was putting in a ATI 4830 and new 650watt PSU (currently had a ATI HD 2600XT) and the MOBO ended up frying and not once but twice (returned the pc and got a new one) So after the PSU checking out ok and the videocard not I got the videocard replaced.

Now the MOBO and old PSU was only using the 20pin connector to the mobo and the new psu I plugged in using the 20+4 pin connector when it fried. Im hoping it was just a bad videocard (4830) as it was tested and didnt work but wouldve plugging in the extra 4pin make it the mobo fry? (fried along the firewire/ usb connectors) Ended up replacing the mobo totally with a Gigabyte and new videocard and its working fine now.

Another question I need an answer to is about the other gateway pc since it uses the same ECS mobo and I got the old videocard RMA'd and back and a new 500watt psu as well for the pc. Do I risk plugging in the 20+4 pin connector and videocard's 6pin or just use the way its currently plugged in with the 20pin minus the 4pin and the videocard plugged in with its 6pin?

Just worried the fault might have been using the new PSU with the 20+4pin when it wasnt using it before. Or was it maybe the videocard bveing bad?
Anyone ever have an issue like that?
If that all makes any sense.