I've got a weird one, my aftermarket Stereo suddenly lost power recently, so I checked the fuses visually and via the light check and all fuses are okay. All connections were all secure too. Tried putting another aftermarket unit in, no power to that either. However, when I put the original Skoda radio in, it works perfectly... So in short, the original stereo runs but aftermarket units don't.. any ideas to fix this issue?

One of the fuses has probably gone. Fuse 10 or fuse 45. If you have a multimeter can check power on the wires on the black ISO connector. Pin 4 and pin 7.