|The drivers for home-premium should be 100% compatible with ultimate as they are both effectivley the same OS.|
Although unlikely, have you changed the OS architecutre (32 bit) to (64 bit). This would cause problems as most drivers are quite specific.
To find out what architecutre your computer is using, right click my computer and select properties. Beside "System type:" it should either say 32 bit operating system or 64 bit operating system.
Nearlly all manufacturers are creating 32-bit drivers, and since your computer is quite new (i5), there is a good chance that there are 64-bit drivers.
My advice would be to download the home-premium drivers, and make sure that you download the correct drivers for your architecture.