sue duck OIL LIGHTON AUDI A3

Hi. Just new to this site. I have an Audi A3 1.8 Turbo sport. 1997. I have had it off the road for 6 month. I put it back on the road yesterday and when I gave it some revs the oil light came on. I have changed the oil pressure switch. I have taken the sump off and checked to see if there was any dirt in the pick up filter. there was none. It was as clean as a whistle. I have cleaned the pressure valve, nothing there. The big ends are OK. I have done everything I can think of and the light still comes on. Does anyone have any suggestions please