To have an  iMac at home or at your business place is a wonderful thing. Once set it runs for years and years. Time machine backs up your data beautifully to an external drive. Printers and scanners once installed works just fine. But over the years it tend to develop some technical issues like pop-ups, slow response times to clicks, noisy fans etc.

Whatever is your issue we it all.

The issue could be due to failing hardware such as Display, Hard Drive or Wireless Adapter. Sometimes a reinstallation of the operating system will fix the issues.