flashes between maximise and restore down repeatedly

[dazormshaw]

i could be sat using my pc and all of a sudden the screen will swith to restore down, sometimes it will just stay like that but most of the time it will then flick back to maximised or almost full screen and it will repeat this cycle until i manage to close the programme down, i could be using firefox, internet explorer or just in windows explorer (it may happen in other programmes but i havent had it occur yet) as you can imagine it can be quite annoying especially if you are part way through typing something!
has anyone come across this before or have any ideas what i can do to stop it

Thanks in advance
Daz