How to repair a dell optiplex dead motherboard with amber light

[cobbinahemmanuel]

Hello, i have a dell optiplex GX620,i have a yellow/amber steady light when ever i on the PC.i have changed the ram,unplugged the PSU from the MoBo,blow the cooling fan,reapplied thermal paste between the processor and the heatsink.No swells on the capacitor.but still has steady amber light on both MoBo and the Power lead.any help pls if dead MoBo too how can i repair it pls

 

[Emerald]

are you sure it is not a bad PSU?

 

[cobbinahemmanuel]

after reseating the CMOS battery i now have blinking amber light when i turn it off and for while i started having steady amber light on both the Power Led and Mobo with speeding fan