Comment 116 for bug 431217

I'm having this problem but in a critical way. I've had to flash back to a 10.04 install of ubuntu, and I am now near the end of an upgrade to 10.10, however, the install has stopped! I have the upgrade window with the status bar (about 18 minutes remaining), and the Terminal text box has opened below this even though I closed it just a few minutes ago. The last line is:

Preparing to replace ttf-mscorefonts-installer 3.2 (using .../ttf-mscorefonts-installer_3.2ubuntu2_all.deb) ...
Then the cursor in the form of an empty box.

Behind this window, though, is what appears to be an End-User License Agreement, BUT I CANNOT SEE IT! I can only see the left edge of the underlying window. Neither the top window nor the bottom window will move. The Terminal will not collapse. Pressing "enter" accomplishes nothing.

What am I supposed to do? Poweroff the machine during the upgrade?