My PC used to be on 24/7 until I decided that I wasting power however now it seems to want to close down at 23:15 unless it is actually working on something - This is annoying me and I would like to know what is causing this shutdown - does anyone have an explanation?
I checked the power options and under Sleep I only have two options - Sleep after which is set at Never and Allow wake timers which is set at Disable - no other options as per your pic!
Any other things i might look at?
You could try unticking 'allow this device to wake the computer' which I know is different to shutting it down but it could bear some relation. I'd also try running a virus/malware scan and also check your bios to see if anything related has changed in there (sometimes there are timer settings in the bios).