ATX POWER SUPPLY ( NO POWER ) ?????? HELP

I Bought 2 new Enlight cases 1 with 300w
1 with 350w. I can't get power to CPU, cpu fans
case fans off of the motherboard. I have turned
the power panel wire around a million time to check
for pos-neg polarity no change . I thought that
maybe something in bios was locked up so I shorted
out the CMOS Bat contacts , no change!
The power up switch turns on the pwer supply
but no juice to the cpu fan so I immediately shut down
so not to fry!
I can press the power sw for the 4 sec , and the
power shuts down. I am getting power out of the
other wires coming out of the supply because
I used a 4to 3 adapter an plugged it in to the
CPU fan an it runs fine. I have tried ever possible
combination using both cases & pwr supply
and two different motherboards
#1 ASUS P2B ( that was working when I took
it out.)

# 2 a brand new A7A266 ASUS

ON both I only have CPU VIDEO RAM installed!
Do I need to have the floppy, HDs, hooked up?

could both of these power units be defective?

I have a older Enlight ATX case 300w that I
pulled the P2B out of and put a P3V4x in hooked
yhe wires up according to the manual an it fired
right up. I Feel like a complete A#$% hole at this
point. I have never had a hardware problem like
this. Please someone help! It has got to be something
I am doing WRONG!!!!!!
Any help would be GREATLY APPRECIATED!!

Thanks