Thanks for the info. I tried installing that theme but still the same problem.
When I initially boot up the device and tap into the password box the normal sized virtual keyboard appears over the top half of the screen. So I can type the password but nothing appears in the password text box underneath the keyboard. Then the keyboard disappears and if I tap into the password text box again the tiny keyboard appears. If I then tap on the keyboard keys (that I cannot see the letters/numbers on) it does put characters into the password text box but they are incorrect because I cannot see what I am typing.