Title pretty much says it all. I’ve had the computer since February and it stopped sleeping a couple weeks ago. I’ve checked the processes in the task manager and googled the ones that didn’t look familiar, but didn’t find anything obvious. I have a button on my keyboard that I can push to put it to sleep, but when I push it the computer sleeps for a couple seconds and then comes back on. Is there an easy way to diagnose this, like a freeware program? Thanks.
This may solve your problem if your computer is hooked up to a network.
Try right clicking on your “My Computer” icon. Choose “Properties” from the context menu. Click on the “Hardware” tab. Click on the “Device Manager” button. Click on the plus sign next to “Network Adapters”. Right click on each item in the list, and choose “Properties”. If there is a “Power Management” tab, click on that and make sure that the “Allow this device to bring the computer out of standby” box is UN-checked.
Could your mouse be ‘jumpy’? Overly sensitive to any kind of movement or vibration?
Pull the ball out of your mouse. Or if a lazer flip it on it’s back and see what happens.
Just a thought. Probably not it but easy to test.
When your computer powers up, there is a way to get into the BIOS settings program (usually by holding down a key, like F2). Do this.
Then look thru the BIOS settings to find one related to power management. Usually there is an option to turn off sleep mode/hibernation/stand by. Make sure that this option is not turned on.
That’s unlikely, if this just started, and you’re absolutely sure that nobody else in the house might have somehow changed the BIOS settings. But it only takes a couple of minutes to check and make sure. And I have heard of (rare) cases where a power surge or dying battery or something caused BIOS settings to change ‘on their own’.
You’ve got to have a routine if you want your computer to go to sleep - it’s no use playing games or watching videos and then expecting it to settle down straight away. It will be too excited. Web-browsing is ill-advised, an certainly not those sorts of websites. Some quiet emails and wordprocessing for about half an hour before sleeptime will help, and maybe a warm milk drink…
No
Ok, the issue will probably be a device that is preventing ACPI sleep/hibernate. Have you added any new hardware or updated drivers? Check the event log - you may be able to see messages from a service or driver that is preventing sleep.
Also, check your pagefile and hibernation file (you need at least as much space in your hibernation file as you have memory). Actually - try deleting the hibernate.sys file (it’s a system+hidden file, usually in C:\ folder. It can get locked and screw things up, too.
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Your computer is wired up. 
It sounds like a device that is allowed to wake the computer is staying active. Sometimes a little vibration picked up the mouse causes this.
In my case, a .NET service was quietly running, not enough to show significant CPU activity, but enough that it prevented the computer from going into sleep or hibernate modes. Eventually (I think after about 60 hours of uptime) the service finished its tasks and went away on its own.