Hello
the default controllers for Windows 2012 are E1000e and LSI Logic SAS, but the older e1000 and LSI parallel should also work fine (they are supported by ESX and AFAIK by Windows too)
I suppose your gut feeling is true. Since you have managed to get rid of xen.sys, there might be something more like that (I had no idea Xen had special tools for Windows!)
Can you managed to boot in safe mode and confirm manually each driver load?
HTH
Plamen