My wifi on my imac has suddenly stopped working I have the wifi exclamation mark when I try to log into my network it shows a strong signal but no joy. My macbook and iphone work fine

Question

WWifi exclamation mark had suddenly appeared on my imac. I  have rebooted imac and router

Answer 1

When you see an exclamation point in the Wi-Fi menu, first turn Wi-Fi off and back on. If it still fails to connect, then from the menu bar, select
           ▹ System Preferences... ▹ Network
Click the Assist me button and select Assistant. Follow the prompts. You may get a warning that Wi-Fi is not available, that you're too far from the base station, or that you're using the wrong password.
Assuming that you've ruled out those possibilities, restart the computer and try again. If there's no change, click the lock icon in the lower left corner of the preference pane and authenticate, if necessary. From the Location menu at the top of the window, select Edit Locations. A sheet will drop down. Click the plus-sign button to create a new location. Give it any name you want. In the new location, set up the Wi-Fi service with the same settings you used before. Click Apply and test.
If there's still no connection, and if you have control of the router, compare its settings to Apple's recommendations. Some third-party routers may be incompatible in 802.11b/g/n radio mode. Try setting the mode to 802.11n only.