You normally need to press one of the keys across the top of the keyboard to get it to work. They key will often have a small "monitor" icon on it.
This will often be the keys that have F1, F2, F3 on them as well.
I have had a look on the interent and I THINK you may need to press the F1 key, if not that the one with the monitor logo on it, or then try all the keys across the top.



