If Mikes suggestion doesn’t work try resetting the screen resolution to a higher resolution. Right click on your desktop in an empty space and choose properties on the pop up menu. Choose settings and then reset to a hiher setting. This will make everything smaller and you should see the window. Move the window back into the middle of the screen. Then redo the settings to your original.
If you are already at your highest resolution you are SOL. Just kidding! You might try rebooting Vegas while holding the shift key. That resets everything to factory default and your window will be back in place. BEWARE – you will lose any custom settings you have applied. Also I always forget wheteher it is shift or ctrl or alt but I believe it is shift.