My nikon d300s CF slot is not working?

My nikon d300s CF slot is not working?

Bad pin, broken connector, bad card… All things that could be wrong.

It'll have to be professionally repaired. That could mean a trip to Nikon if you can't find a local shop.

Try a different memory card, if that doesn't work spray VERY little amount of electrical contact cleaner inside the memory card slot, let is dry well, repeat a couple of times and try again when camera is fully dry. Make sure camera is turned off while there's contact cleaner in it.