how do i stop itunes re-opening when I close it down

I have had a problem for some time where most evenings when I close iTunes it re-opens once, or twice, sometimes three times.

Today I did the latest iTunes update and now iTunes re-opens itself immediately - has happened 8 times now so will resort to using task manager to end task so I can cleanly shut my pc down but any advice gratefully received.

Windows 8.1.

I don't experience this on my Surface 3 or my Ultrabook (both of which I updated today and used iTunes on to test), just my HP all in one 'desktop'.