Thanks but how do I switch on the Fn lock when I don't have an Fn lock key? (FYI: my computer is a Lenovo G50.) Is this the answer:

"1. Press the power button to turn your computer on
2. Press F10 key to enter BIOS setup screen
3. Use the left right arrow keys to navigate to “System Configuration”
4. Use the up down arrow keys to navigate to the “action keys Mode”
5. Press “Enter” to open the Enabled / Disabled menu
6. Use up down arrow keys to select “Disable”
7. Press the F10 key
8. Use arrow keys to select “Yes”
9. Press “Enter” to save changes and start windows" ??