Half my screen has disappeared!

An client of mine who provides interim financial management solutions for very large companies (FTSE 100) phoned me up one day.

"Ruairi, I'm in terrible trouble!"

"What's up?"

"Half my screen has disappeared!"

"OK, can you see the Start button and the time?"

"Yes. It's Excel, half the screen has gone!"

"OK, can you see the Microsoft Excel title at the top and the X to close the window at the top right?"

"I can only see the Microsoft Excel part."

"Uh, ok, have you moved the window to the right or something?"

"How do I do that?"

"Click and hold the left mouse button at the top of the window where the blue strip is, then move the mouse to reposition it."

"Goodness me you're a genius, I don't know how we'd cope without you!"

This is after using PC's for around 15 years. Amazing! :)