Keyboard + Display Unusual behaviour

[UnusedName]

Hi,
Installed Mint a few weeks back and have come across some unusual behaviour.
1. When using firefox, I click on a menu e.g. File and once I drag the mouse down the menu it disappears.
2. When using google earth I cannot type anything into the Fly To section
3. If I open up a terminal window while firefox is open I cannot type into the terminal window
Funnily though, when I initially installed everything was OK.
I reinstalled Mint and all was ok again for a while - but broken again.
I have not installed any updates / packages / applications in the mean time.
Has anyone else come across this or have any ideas for me?
Thanks.