Thank you for your message. Does the power button light pulse when the system goes to sleep mode?
Does the computer not respond when in sleep mode irrespective of the AC adapter being connected or not? Does it happen only when the AC adapter is disconnected?
Restart the computer & tap F2 to get into BIOS, click power management – USB wake support – Check the box Wake on USB
Click sleep mode & check what option is enabled IS OS automatic selection or force S3.
For my reference, please click on the message tab next to your avatar– click “New Message” & search for my Dell username (Sreejith R) & send a private message with the service tag, registered name & email address.