Psu problem, how to fix?

It never ceases to amaze me how people can skimp on the PSU when that is the very HEART of the computer...

Post specs of both PSU's 12V amperage ratings. In fact, links to the the 1000W and 400W PSU would be nice. Wattage doesn't mean sh**; it's about the AMPERAGE on the rails. I highly suspect the GTX275 draws a heavy amperage on the 12V rail (roughly a minimum of 18A I think).

Swap a new GPU (as long it's low powered, i.e. a 9400GT or something) into the comp and retest - if that works, you're PSU has defective and/or very low 12V amp ratings.

but the psu is still powering because the little onboard-power button is still glowing
A computer PSU has two independent sections: the large, main power section that provides the power to run the computer and a small, 10 - 15 watt, 5 volt power supply that, among other things, powers that motherboard LED. The main section can be toast - melted down into a puddle of molten copper and silicon, but if the standby power supply is good, that little LED will be on.

Oh as a note, i shorted the green and black on the psu as xion recommends, and the psu stays running fan spins and lights are on... so i dont think the psu is blown....
That also does not mean much. It's a very minimal 12 volt load. It doesn't check the 3.3 or 5 volt output. It also does not check a control signal from the PSU to the motherboard called the "PowerOK" signal.

If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby. The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot. The tolerances should be +/- 5%. If not, the PSU is bad.

ok first of all i thought about the gpu already swapped out to no-gpu as in just the board same result, tried it with a VERY old pci express vid card hell i dont even know what it is no external power at all and still dont work...

also i know the psu is important and hence i plan to eventually get a nice bfg etc but for now it was that or not be able to afford the cpu or gpu i wanted and

so its not too much current coming on from the video card,

also i just got back from my buddies house and he swapped out his power pack for the xion and the damn thing booted his computer fine...

ill try to get a multimeter to check things but the fact that it booted his computer makes me believe that its not a "dead" power supply... but the fact that my new mobo etc works with the no-name 400w power supply means the rest is working im kinda at a loss (sorry dont even know the specs for that power pack it doesnt have a brand/ratings etc just a little round sticker that says 400w).. though here are the specs for the 1kw thats not powering my pc

# orm Factor: ATX
# Wattage: 1000-Watt
# Fan: 140 mm
# +3.3V: 24 A
# +5V: 30 A
# +12V 1: 20 A
# +12V 2: 20 A
# +12V 3: 20 A
# +12V 4: 35 A
# +12V 5: 35 A
# +12V 6: 20 A
# +12V Rails: 6
# -12V: 0.5 A
# +5VSB: 5.0 A
# 20+4-Pin Connector: 1
# Motherboard Connector: 20+4 Pin
# 4-Pin/8-Pin EPS Connector: 1
# 6-Pin PCI-Express Connector: 2
# 8-Pin PCI-Express Connector: 2
# 4-Pin Floppy Connector: 1
# 4-Pin Peripheral Connector: 8

Tell us the specs of your friend's pc

tracked down atleast where the problems coming from, if i hook up the 24 pin, but not the 8 pin connector the power comes on, it doesnt boot but the power supply stays running and cpu fan keeps spinning, (ps button doesnt work though either)

so it looks like the source has to do with the 8 pin connector any suggestions?

WTF NOW I HOOKED UP 1 of the 4 pins instead of both and it f*cking started, i could swear i tried this yesterday... can i leave it like this with only 1 of the 4 pins?

ok on a side note and update, i got it working i get the feeling one of the pins on the power pack (4pin) that wasnt probably pushed in all the way or something because i fidgeted with them and now their working and its booted.. f*cking weird