Please, explain a bit better: you have image from composite/RGB port (silly question on an A4000)?
Do you measure the PSU voltages? With a multimeter, of course.... :-P
Not joking: Do you have image only if you set the mode to NTSC and no other modes runs? Reinstall (Windows way of correcting bugs) all the Worbench and the drivers thereafter....:-(
Sounds much for nothing? Then give your Amiga to me. I'll much happy in fix those issues myself... :-D