Mac mini (late 2014, 8GB RAM) has become agonizingly slow to boot up - 16 minutes returned by macOS 10.13.3. Applications (e.g.Pages, Safari) will not start - system returns 'Application Unresponsive'.
I have at least three backups of full system or needed data (Acronis True Image, Time Machine, iCloud)
How do I determine where problem is - Mac mini HD and what to do next - reformat HD (how?) , reinstall macOS (how?) - or...?