Computer won't boot after a Power Supply swap

[TheXephoxify]

Hey i just swapped my old power supply for a new one on my computer and now my computer won't boot again sometimes the fans will turn for a fraction of a second and then nothing i need help

thank you for any help

[camerongray]

Does it work with the old power supply?  What new power supply are you using?  Have you connected all cables to the motherboard including the 4 or 8pin one near to the CPU?  What spec is the rest of the system?

[TheXephoxify]

hey no the old psu doesn't boot the system two I've just tried it and the pc was a dell dimension 8400 and i upgraded the pus to a x-supply 550w and the gpu to some old pci-e 2 i think im not sure of the brand or nothing it wasn't in the box but the computer and gpu were working before the psu swap it just froze because the gpu didn't have enough watts to work and that is why i got a new one so i never had a chance of looking my graphics card name all i can read on it is foxconn E253117 ML 1 and 86801086AA
Thanks for your help

[camerongray]

Given that it doesn't work with both PSUs, what makes you so sure that the issue is PSU related?

Put the machine back to exactly how it was before you started swapping components including removing the video card you added and putting the original one (if any) back.

x-supply 550w

Never heard of that brand, doesn't fill me with confidence over the quality of the unit.

Also, please break your replies up into proper sentences, that was almost impossible to read.

[Geek-9pm]

When working on a motherboard, there is the chance o losing the CMOS settings. It will revert to a set of default settings that cause the thing to stall during boor up.

[TheXephoxify]

cameron gray, i did what you asked me to and it didn't work. Tomorrow i will head out to buy a new power switch just to see. I think it is psu related because it never did that before. and what should i do geek-9pm for the cmos?