Chosen Solution
I have an iMac 8,1 24 inch that will not go into sleep mode. If you click sleep, the screen will stay on. Nothing else seems to be out of the ordinary besides this. As a side note, I did put an SSD in the iMac prior to this issue.
did you follow this guide? iMac Intel 24" EMC 2134 and 2211 Hard Drive Replacement, jump down to Step 20 and did you transfer the sensor to your SSD? If not that’s likely the cause!
