New psu no boot??

[dae_amp_ika_dtp]

hi. im running a new 450 watt hercules psu. the system im trying to power up specs are:

1.2 amd athlon
2x512mbsdram
1x128mb sdram
100gb maxtor 7200
10gb seagate 5400
dvd rw drive
dvd rom drive
floppy disk drive
evga geforce fx5200 128mb
pci network card
pci modem
pci sound card
msi-6330v2 motherboard(made for gateway oem)

the new power supply one turns the power led on. i see no sign of it trying to turn on the processor. the old power supply works fine. what i noticed is the old power supply mombo connecter has all 20 pins. the new one i bought only has 19. but the new one i have has a connecter for a p4 machine. is this where that one pin went? do you think the missing pin is because its meant for a p4? so the missing pin is to start up the processor? i have a picture of the mombo connecters. when the missing psu pin goes

is that pin for the processor? i have no clue. its missing from the power supply connector to the mombo. not missing on the mombo. is there a way i can fix this? any help would be greatly apreciated. thanks.

oh yeah. and what would be the minimum wattage psu for my setup? thanks