Upgrading Precision 670 from 8.0 to 8.1

I was able to install Windows 8.0 onto my Precision 670 and have been using it for a while without problem.

However, when I try to upgrade the operation system to 8.1, I get the following errors:

You can't install Windows 8.1 because your processor doesn't support LAHF/SAHF

You can't install Windows 8.1 because your processor doesn't support PrefetchW.

I seem to remember having a similar problem when trying to install Windows 8.0 but a later release of Windows 8.0 did install; but only a few weeks later. The error above has been there since October and shows no sign of going away

Does anyone know if there is a workaround?

There must be loads of people who still use Precision 670s and I fail to understand why Microsoft would block using 8.1 for this model (or its processor).

Thank you (in advance)

Tony