If it were me I would disconnect the battery for 30 minutes and see what happens. I wouldn't have thought it would do any harm, then again these BMW's have a mind of their own.

Check all your fuses, though I think you may have already done that.

Any other symptoms ? Even in things seemingly nothing to do with the radio ?

Check all connections in the trunk area are firmly connected.

After that, I'd be looking at the head unit. Is there even power getting to it ? The absence of the orange light suggests not.

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2001 X5 4.4i