Mac Mini M2 won't stay in sleep

My three month old Mac Mini running Ventura running 13.3.1 (a) has suddenly refused to stay asleep. It will awake within 3 - 15 seconds after putting it to sleep. This only started yesterday. I've rebooted a couple of times with no change. I can't be sure but is seem to happen after Safari locked up. It wouldn't close. No apps would close and when I went to the Apple menu to choose force quit, the menus wouldn't stay open long enough to do anything. The computer started clicking so I pressed the switch till it turned off.

Now it won't stay in sleep. Activity monitor doesn't show me any odd apps taking CPU time. The apps are Apple ones or Adobe. I'm a Creative Cloud user.

I've turned off time machine and booted without any standard apps like mail or messages running to no avail.

When looking through system settings I noticed that I'm supposed to have a screen save pop up after 20 minutes. That has never happened on this machine. I never thought twice about it because I never ran a screen saver on my old Mac and I assumed the settings were carried over to this one.

I used to be able to turn off the screen by moving the mouse to a corner of the screen on my old iMac and I notice that this does't appear to work here either.

Any ideas?