If you run SketchUp with multiple monitors, this may happen to you. You start up the software and see its icon in the task bar, but there aren't any windows to be seen.
The software actually started OK, but the main window is off-screen.
To reset the window position, run
regedit and go to
HKCUSoftwareGoogleSketchUp8CSkDialogx and set the value to 0. If that doesn't work, look for another key with
Dlg in it.