Windows 7: Help desperately needed!

I just installed a new PSU, but nothing happens when I switch on my PC. There is a green light that comes on, on the motherboard, but that's it. Can you guys please help me!!

I'm going to state the obvious first, sorry

Are all neccessary cables plugged in? GFX, CPU etc.

Also (if i remember rightly) is there a voltage switch on the back of the PSU? Is that set right?

I've done that before & created my own mushroom cloud LOL

Yes, I plugged in all the cables the same way as they were before, and there is no voltage switch on the back. (It is set for the correct voltage.)

I just put the old 1 back, and everything works fine.

Does the new PSU is of same watt as the previous one???

No. The old one is 350watt. The new one is 400watt.

I also see that the new one has a lot of extra cables.

Hmm, could it be that the MB doesn't accept above 350watt ? It may have the green light, but it could be that the slots aren't configured for 400+ thus no output

check the power switch connection with the motherboard. It might get loose...
Or just check the PSU, may be the PSU is faulty...

No it is deffinately not that.

If all of the above fail, return it for a replacement.. throwing a new PSU in a box shouldn't be causing you all this grief... its beginning to sound like a faulty unit..

??? Not.