I have a gigabyte EP45-UD3P motherboard, and for a while I've been having this issue.
Basically when I try to put the PC into sleep mode, it shuts off and then repeatedly cycles on and off again. I can hear the fans spinning up for 2 or 3 seconds, all the lights come on, then it powers off again. It keeps cycling like that until I turn off the power supply switch.
Wondering if anyone else has had issues like this. I believe it to be an issue with the motherboard. Nothing has changed in the system recently.
Won't go into Standby or Sleep? If you have a Gigabyte I won't be too surprised. To simplify, in the BIOS I'd Load Defaults (Optimized for GA), and re-institute your other settings: AHCI, CPU Fan, RAM, etc <or> make certain (S3) is Enabled in the BIOS.
For the most part, ignore most of the USB warnings.
Also, if you have 'Media Sharing' enabled then that will easily keep a PC from sleeping.
Check your Power Management Options on your Control Panel (Start, Control Panel, Power Settings, Change plan settings, Change advanced power settings).
-> “Multimedia settings” option, “When sharing media.” ->”Allow the computer to sleep."