Question : Problem: mac mini hangs on startup

My mac mini hangs on start up -everything ok till this week - apple logo, grey screen, spinning wheel goes on for ever - however I can get into the machine on the network from my imac to look at files in the mac mini, but cannot get in via screen sharing.

tried pressing c on startup also tried shift but nothing changes

Answer : Problem: mac mini hangs on startup

thanks for your prompt suggestions