How to reset SMU

My iMac starts Ok and sign in OK until all the desktop elements are are inplace but once i press the mouse the dreaded rainbow wheel arrears and pointing at any software it become in active (dim light) and the wheel continues going round and round . Safe boot has not resolved the issue. I was told to reset SMU

Now the are two ways to do it a0 by taking all cables out wait 15 second put everything back and reboot. This did not resolve the issue

b0 to physically to reset SMU that is where I thought this site would be helpful

BUT SMU is not on the guide menu

Can you possible help ??