No beeps, no post, no display...

[JayJayJedi]

I'm having a bit of trouble with booting up the system. I can hear the HDD running, CPU fan is spinning as usual, there are no beeps & no display. Since I don't have a desktop case yet, it's currently running on testbench. And I've also noticed that it turns on whenever I flick the switch on the PSU (without having to press the power switch).
The specs are:
Gigabyte GA-7ZX rev. 5.00
AMD Duron 1300
2x 128 MB SDRAM
3dfx Voodoo 3 3000 AGP
Sound Blaster Pro 2 ISA
150Gb HDD WD
Trust PowerMaster 420 W PSU

[eeeee1]

any debug lights?

[8-Bit Ninja]

Have you got onboard graphics? Given how old that stuff is id check to see if any caps have leaked on the motherboard and graphics card 

[JayJayJedi]

No, there's no onboard graphics, just onboard sound, but that's disabled.

[JayJayJedi]

6 minutes ago, eeeee1 said:

any debug lights?

No, there's only one green LED and it turns on as soon as the power is switched on...

[8-Bit Ninja]

3 minutes ago, JayJayJedi said:

No, there's no onboard graphics, just onboard sound, but that's disabled.

have you got another compatible graphics card, if not visually inspect the motherboard and the graphics card for any leakage from the capacitor 

[JayJayJedi]

10 minutes ago, 8-Bit Ninja said:

have you got another compatible graphics card, if not visually inspect the motherboard and the graphics card for any leakage from the capacitor 

No, asked a few of my friends to check if they have any spare AGP cards. I've already checked & there's no leakage. And compatibility shouldn't be an issue here, 'cause I've checked for this CPU and it should be supported by the board.

[JayJayJedi]

Finally got my POST card and here are the results (and they're the same on both motherboards).

[JayJayJedi]

Still no success. Tested 3 processors (Duron 950, Duron 1.2 & Duron 1.3) on 4 diff. motherboards (GA-7ZX (rev. 1.01) , GA-7ZX (rev. 5.00) & 2x GA-7IXE4 (rev. 1.00)), with 2x 128 or 2x 256 SDRAM still no POST, perhaps just once in approx. 60 boot ups & that's it. Used a bit older PSU as provided in the picture & a bit newer one from Chieftec (750w), still the same. I figured if there would be anything wrong with graphics card (3dfx voodoo3 3000) or even CPU or something, I'd get some damn beep from the speaker, but nothing; monitor just keeps blinking.

[JayJayJedi]

I've tested with a motherboard that I borrowed; graphics card, sound card, RAM & PSU work fine. Guess it's now down to CPU & motherboard. Someone has mentioned that I have to check about multiplyer & fsb speed settings, but I can't find any jumpers, only FSB switch which is already set to 100 MHz as listed for those Durons