Would have 12 and 5 Volts so nothing a miss there. There are many reasons for an old PC to require this power up. From an old CMOS battery, bad caps (google that) to other aging parts. Since there is little known about this PC, start by changing the cheapest part first (like that CMOS battery.)
For some time now, my PC starts only after I power it up twice.
First, all fans and leds are up but no bios post. Then I shut it down from the button and power it up again. Then it works.
I susspected a power surge and when I touched my chasis from outside or my usb outlets I felt electrical current. I then susspected a bad grounding in my house (I live with rent). So I got a cable, connected from power socked outlet ground to my heat pipes. Then no current.
But the PC problem persists.
Today I opened my chasis and measured the voltage between molex and other components.
I tryied dvd rom screws, cpu metalic radiator etc. Everywhere I got 5/12 volts, depending on molex pin tryed. Then I checked between my molex and my home made ground connection in the power socked. Again, 12/5 V.
What this means?This cannot be ok.... But at least I know my ground connection is working.
le : my PSU is an Antec EDG650, 650W.