Renault Clio 1.4 T Reg 1999. Gearbox Problem?

I have got Renault Clio Mk2 1.6 Automatic and why does the lights comes on?
When I am driving around 50mph or above sometime it just bang and stuck in the 3rd gear and won't kickback or change it when I put it number 1 or 2 unless I turn the engine off and back on.

The light is the gearstick and auto underneath which mean there is a faulty transmission. I have changed the transmission fluid and now I have found out one of my driveshaft is knocking, could that be the reason?

Tas
March 2009