Shut off your water supply and disconnect the 1/4" line that feeds to RO unit. Turn the water on and make sure you have flow. If so then remove the prefilter from its housing, reconnect the line and see if you have RO flow yet. If not try removing the carbon and do the same thing but only for a few minutes as chlorine wil damage the membrane given time.
Its usually the self piercing needle valve that is the culprit.
Do you know what your water pressure and water temperature are? What is the waste ratio? Try pinching the waste line temporarily to see if that gets you flow. If you have a flush kit, which are worthless by the way, make sure its not in the bypass position.
I have lots more tips if these don't work.