after trying to flash the tablet several times, using a completely idiotic sequence to enable the firmware update (hold vol key, press on key several times bla bla) the tablet booted up again. I didn't flash it. Some combination of keys got it out of the blank screen state somehow.
So, I'm back to the the "the process com.android.phone has stopped" stage. Well, at least I didn't fry the video hardware.
I'm also amazed at how inept the idiots who wrote android are. My tablet doesn't have a phone and yet the phone app is running wasting resources, and if it's deleted the OS is so dumb it's unable to just ignore the missing files carry on.