Motorcycle Questions? Ask a Mechanic.
Hi and thank you for your question.
The first thing this sounds like is the clutch is slipping and is causing you to loose all forward drive through the transmission. If you still have normal spring tension in the clotch lever, you are going to have to pull the clutch side cover off and see what is going on under there.
The symptom of the gear indicator jumping around sounds like the sensor plate or contact under it have a problem. I would suggest taking a look at the clutch first, then after the whole lack of forward drive is resolved, the gear indicator can be addressed.