edgy upgrade problems

[MLT]

I have just updated my dapper system to edgy and have some very strange 
problems that I suspect are related but do not know how.  The system is an 
AMD64 system on an asus motherboard A8N-VM.  This board caused some problems 
in dapper until I updated the bios.  There are no more updates of the bios 
available

When I boot messages are as normal except for a message at the bottom saying:

Kernel direct mapping tables up to 1000 0000 @ 8000-8000

Then at the point I would expect usplash to start the screen blanks and I am 
left with a white cursor in the top left.

If I change to tty1 then I get the following error message:

5e411d60:4c7d4512 F1 ILLEGAL X86 OPCODE!

It then notifies me that the 4 logical volume are now active and then the 
following message:

5e411d60:4c7d4512 63 ILLEGAL X86 OPCODE!

The computer then seems to do a complete check of the file system which the 
system passes.  The system then does a very slow boot to an x terminal, there 
are no errors posted during this process.

The system then goes into kdm which will accept input for a short time (I 
think until a return key is pressed) then the keyboard is ignored for x or a 
console and there is no acceptance of any other USB input.  The machine will 
then boot properly but no input is possible.  It is possible to login from a 
ssh session but there is no bash/dash shell just a “dumb” $.

I have tried booting with acpi=off noapic and this has not solved the problem.

I have also tried reinstalling the packages making up the ubuntu-minimal and 
ubuntu *standard metapackages and this has not improved matters.

In addition I have used a beta1 edgy livecd which would not boot past the 
first error message as outlined above.  This was also tried with noapic 
acpi=off.

At this point my knowledge stops.  Any suggestions?

Is there a painless way I can go back to dapper without losing the settings I 
have, painfully, managed to set on the machine?

Thanks,

Mlt