Hello mate.
Funny you should say that. I have an aftermarket unit fitted, but mine has just done the same after the battery went totally flat and was recharged. Haven't looked into it yet, but I know it is receiving a permanent 12v supply, and I was suspecting that I'd somehow lost the switched ignition 12v supply. You say there was no fuse on this line?? Hmmmm.... I'm going to look at mine tomorrow, so if I find anything I'll let you know. Likewise, could you give me a shout if you find anything elightening. Cheers......