I've got an old system that I'm using for some CAD work.

The system is a Gigabyte GA 7ZX motherboard with Socket A for AMD Duron/Athlon processor; a VIA KT133/686A chipset, with support for PC133 SDRAM .

I did something very simple ---- I replaced the CPU Duron 900 with a Duron 1200 and I added a stick of 256 memory. I made sure that the CPU and memory pieces were compatible with the motherboard.

The machine will not pass the POST.

I took out the memory and put the old processor back in......no POST
I took all peripherals off line and added them one at a time.....no POST
I replaced the power supply......no Post
I replaced the motherboard with a brand new one exact model.....no POST
I pulled the video card and checked it.......no POST
I switched the new CPU back in.....no POST
I switched out the memory sticks one at a time....no POST

I'm stumped, any ideas.

clear the cmos.