iMac won't search for trackpad and keyboard after restart

I've recently experienced problems using the trackpad and keyboard to wake up my iMac. Twice in the last 2 months we have been unable to wake the mac, so we would use the power button to restart it, and when it came back on again the keyboard and trackpad would be fine.

However, the same thing happened yesterday and when we restarted the mac it refused to search for the bluetooth trackpad and keyboard. normally if we have an issue we'd get the "connection lost" then "connected' message, but none of that is happening. Both devices are on, and the batteries are fine. I've tried using a usb mouse but there's no response with that either. We're stuck on the log in screen