iMac problems
iMac is taking too long to start up?
iMac, iOS 11.0.3
First off please fix your Communities Profile, iMac's do not run iOS they run macOS.
Next we need to know what year model iMac and what version of macOS is it running?
see > Identify your iMac - Apple Support
Then after that we will need to know exactly what external devices you have plugged in and what third party software you have installed on your iMac?
If that sound hard, then you can easily post all of that information by simply running and posting an EtreCheck report.
see > http://etrecheck.com/