ATX powersupply

[Ranjya]

Hi,
I have a old i810e PC working on 12 pin AT SMPS.
There is a ATX powersupply 20 pin connector also.
Recently I connected a ATX 20 pin SMPS.
When I supply power....both the Power LED and HDD LED
light up.
When I press the front Power on switch nothing
happens i.e neither the SMPS fan nor processor fan
start.
What am I doing wrong.
P.S: This is all in preparation of building a new PC.

[jagadeesh.k750i]

see that the power sense cable from cpu box is connected to mother board, you migt have not connected ,read mother board manual.