PD 4.0 with boot camp partition

I've been running PD 3.0 with a Boot Camp partition fine for ages and I've upgraded to PD 4.0 today and I'm now working on reverting back to PD 3.0. Windows keeps hanging on me now, and I've lost audio support. The hanging will last for several minutes and then just start operating normally again. I've try starting up a program or closing a window, and then it'll start all over again. I've tried uninstalling and reinstalling Parallels Tools, but that hasn't help yet. I checked the CPU usage on the Mac and it's barely registering any activity. With regards to the audio problem, I've tried enabling, re-enabling the Sounds support, I've tried changing output device to each of the available options: Default, Built-in Output, Null device, none of which have helped.

I'm going to try again from scratch using a backed up image of my boot camp partition and see if there's something I'm botching up in the process.