I'm running Windows 7 64-bit on a Lenovo laptop, and I have a problem wherein after I've put it to 'sleep' once, it will seemingly without any reason or warning go back to sleep every 10 to 15 minutes after that.
Each time it wakes back up just fine, and you can happily continue on. However, 10 or 15 minutes later, it just drops out into sleep mode.
I don't see any errors in the system logs. I don't think it's related to heat ( since it's not rebooting ).
When I check the system event log, I can see where the machine goes to sleep, but it simply says "reason: application API", and doesn't indicate which app ( brilliant ). I don't see any errors from hardware or anything relating to sleep in the application log that would point to what is going on either.
How can I find out which app is triggering this?
EDIT: I confirmed that temperature wasn't the issue. I think it's important to keep in mind that this condition only happens after the first sleep. If I reboot, the problem goes away until I put it to sleep, after which it sleeps on it's own every few minutes. Is there no way to capture which app is calling the sleep routine?
+ R, type 
Best Answer
I had exactly the same problem. Lenovo, Windows 7. After the first suspend, machine goes to sleep automatically ("reason: application API" ;) ).
In my case the Lenovo PM Service was the problem.
After disabling this service (using msconfig) the problem disappeared.
The same link (http://answers.microsoft.com/en-us/ie/forum/ie8-windows_other/windows-goes-into-sleep-mode-on-its-own-while/9017bdac-9fef-4f7c-9e56-47976d30b7e3), as in previous answer, was helpful.
Addendum: I have installed the latest software from Lenovo: Lenovo Power Management Driver for Windows 7 (v.1.65.05.21), Power Manager for Windows 7 (v.6.45). I have installed the latest BIOS (v.3.25) in my T500. Unfortunately, it does not help. The only solution is - Lenovo PM Service disabled.