“Something wrong with all my fingernails on both hands?”

I have always had pink healthy nails. In April this year, all my fingernails suddenly started to look dirty like I had been gardening. My nails have not grown at all since April this year - I don't mean they have snapped off, but they have stopped growing. It is getting worse and worse. The nails are abnormal all around where they join the finger. I can't find out what is wrong. Please can you give your expert opinion? Many thanks. I am 70, female and fit and healthy - no illness, don't drink or smoke, not overweight. Toenails are unaffected. I thought it might be a Biotin deficiency and have been taking Biotin but it has not helped at all.