Hi
I'm not sure we can help out here - it sounds like the lack of an up-to-date Windows 8 graphics driver is the issue.
I'd suggest contacting Sony to see what their support plans are for this model. You can do this here
http://www.sony.co.uk/support/en/contacts/vaio/email
The only other thing I can suggest is when you just have the Nvidia driver active try and install the latest Nvidia Windows 8 driver.
Regards,
James