Apply Vicks Vaspour rub to toes and nails at night, cover with socks each night before bed. You will be amazed how this clears up discoloured and mis-shapen nails like nothing else
Methylated spirits. Just apply to (in my case toenails) with cotton wool every day. I was desperate but it seems to be working. Read this tip from doc in Oldie Magazine.
Rub tea tree oil on the affected nail(s). Try to leave it on as long as possible - maybe at night with cotton gloves, because it does smell pretty strong.