i got it to freeze by suspending a machine and then trying to stop it from the suspended state.
turned on the VT-x extensions and now can not reboot it in 9 cases out of 10. in the one case when i reboot it i have a severely restricted set of vesa modes to use. what's interesting is that i need to reboot osx itself for parallels to _really_ turn vt-x off and allow me to use the video properly.