I've picked up a secondhand copy of Guitar Hero 3 Legends of Rock today along with the guitar.

How do I sync the guitar as I have no instructions with it.

I've tried pushing the Playstation button and a row of red lioghts flash for some seconds then go off but no sync.

I have no experience with the Guitar Hero guitar, but see if you can find another button. I know that on the Rock Band guitar, the sync button is not the PS button since it uses a USB dongle and not the integrated Bluetooth.