Motherboard is : ASUS A7N8X-E Deluxe, Rev1.01,

On start up get: "cmos checksum error - defaults loaded" error BIOS is reset everytime and can't boot to Windows off HDD.

POST report is ok once I tell it there is no Floppy drive attached and not to seek it. The boot sequence starts then just as get to load windows safe mode options whole PC shuts down. BIOS is reset to defaults again.

I've checked the battery and jumpers. Tried a known working battery. Changed Graphics card, changed memory, changed HD to one without an OS. Disconnected DVD drive. PSU is known to be ok.

IN BIOS CPU is recognised correctly and memory is also recognised ok.

So is it likely to be a bad motherboard or corrupted BIOS or something else?

Thanks :)