Precision 3520 BIOS issue

Hi,

I picked up a PWM 3520 for spares/repair. The fault is an odd one: I can't change anything in the BIOS, as it's all greyed out as if it's got an admin password. However, it doesn't ask for a password on entry to the BIOS and (just to confuse things) the BIOS setup shows as no password set at all.

If I make set a password, it says it's done it, but on reboot it says not set again. The one or two options I can tick, won't stay ticked on reboot. However, the date and time are settable and it holds them.

I've replaced the BIOS battery twice, I've tried upgrading, and downgrading the BIOS to which I am told "firmware update failed rebooting your system" with no error message anywhere (not even the logs). I've tried with and without the main battery, I've every key combination I can find on the internet, but nothing has improved.

I'm fairly well reigned to a new motherboard (as this is waaaaaaaaaaaaaay out of warranty) but thought I'd check here, just in case, before taking that route.

So.....

Anyone got any ideas please?

Thanks

Alex