Auto sleep Macbook Late 2008

Question

HelloI am facing strange issue on my macbook (late 2008) OS x 10.11.14my macbook is entering sleep mode after every 20 to 25 sec and I can wake it up by pressing brightness increase/decrease key on keyboard only with AC power connected and If I disconnect AC power then brightness increase/decrease key not able to wake it up.I have checked energy saver setting for "computer sleep" and "display sleep" and found that it is already on "never" .so the issue ismacbook entered "Sleep Mode"I pressed brightness increase or decrease key on keyboard with AC power connected and macbook woke upafter 20 to 25 sec macbook entered "Sleep Mode" againSame case in safe mode.Any idea what is wrong with macbook ?

faryaz · Answer

here is some logUUID: AA20490B-CBC5-44FC-BD7C-C4EB9B85CEDF2016-05-03 23:56:10 +1200 Notification        Display is turned off                                                                2016-05-03 23:56:10 +1200 Assertions          PID 55(configd) Summary DenySystemSleep "InternetSharingPreferencePlugin" 00:21:45  id:0x0x70000086f [System: PrevSleep DeclUser kCPU kDisp]          2016-05-03 23:56:10 +1200 Assertions          PID 101(hidd) Summary UserIsActive "com.apple.iohideventsystem.queue.tickle" 01:33:44  id:0x0x90000014c [System: PrevSleep DeclUser kCPU kDisp]          2016-05-03 23:56:10 +1200 Assertions          Kernel Idle sleep preventers: -None-          2016-05-03 23:56:10 +1200 Sleep               Entering DarkWake state due to &#x27;Clamshell Sleep&#x27;: Using AC (Charge:100%) 4 secs    2016-05-03 23:56:12 +1200 Assertions          Kernel Idle sleep preventers: IODisplayWrangler          2016-05-03 23:56:12 +1200 Notification        Display is turned on                                                                 2016-05-03 23:56:14 +1200 Wake                DarkWake to FullWake from Safe Sleep [CDNVA] due to HID Activity: Using AC (Charge:100%)