Answer
According to Microsoft, this is a known issue where the Virtual PC console seems to fall off the edge of the screen. Luckily, Microsoft offers three different solutions.

Solution 1:
Right after you open your Virtual PC, press ALT, left arrow, down arrow, m, left arrow. You'll notice that as soon as you move your mouse, the Virtual PC console will snap back to its default location. Make sure you don't click anywhere right after you open Virtual PC; you want to only press the combination of keys listed above before clicking or typing anything else.

Solution 2:
Edit the options.xml file located at %appdata%\Microsoft\Virtual PC\Options.xml and change the location of the window. For example, run "notepad %appdata%\Microsoft\Virtual PC\Options.xml" and adjust the values for left_position and top_position in the area, which is located under the section. The typical settings in an options.xml file look something like this:

<window>
  <console>
     <height  type="integer">256</height>
     <left_position  type="integer">913</left_position>
     <top_position  type="integer">90</top_position>
     <visible  type="boolean">true</visible>
     <width  type="integer">367</width>
  </console>

Adjusting the settings for the location of the console should restore your console.

Solution 3:
Verify that the Virtual PC is not running. Delete the options.xml file located at %appdata%\Microsoft\Virtual PC\Options.xml. When you restart Virtual PC, you'll get your console back but you'll lose any global configuration settings. If that's a concern, make sure you note down your configuration settings before you delete the file so you can reconfigure them afterward.

Some people may have success with one of the above options but not with the others, so don't hesitate to try another option if one doesn't work. You should have the best luck with solution No. 3.