Just release Windows XP 2, which is just windows xp with security fixes and the latest IE.
Guaranteed they sell more copies than windows vista, 7 and 8 combined.
Plus it comes with a gold embossed certificate that says "We're really sorry about Vista, 7 and 8. Really, really sorry, we apologise unreservedly."
Imagine the reviews: "Its so much faster than Windows 7" and "My new PC is usably fast!" and "I love that Windows now actually includes windows instead of that ugly metro UI".