In-car SatNav

I have a 2012 MX5/NC Venture edition which is fitted with a Sanyo/TomTom NVA SD8110 system. SatNav shows only "No Maps Found". Radio/CD, etc work fine. The person who sold the car said that the problem first presented itself when the car battery was left flat for a few days. Having tried many recommended solutions without success, I'm pretty sure that, there's nothing wrong with the SD card or the data on it. It seems to me now that the unit doesn't see the SD slot at all!
Could anyone recommend an auto electrician/electronics person who might be able to help?
Ta, C.
Could anyone recommend an auto electrician/electronics person who might be able to help?
Ta, C.