Flash has stopped working?

Everything was working fine until I had to spend a few days in hospital. When I came out the camera worked on all functions but Flash would not work in any mode. Changing/re-charging the battery made no difference. I have borrowed an SB 40 flash from a friend and with this mounted Flash function is restored.

Where should I start to look.

PS I am well equiped with tools, meters etc after a sixty year working life in domestic electronics but I am 80 years old and my eyesight is not what it was.