I would request you to try these steps and advise the result,
*Confirm if any changes were made to the system (any software/hardware).
*To check if there are any hardware failure initiate Dell Diagnostics on the system to know what is causing system freezing issue. Restart the system and keep tapping the F12 to initiate Dell diagnostics, if any component has failed then accordingly it will come up with an error code followed with an error message.
*Check if the system BIOS and chipset driver is updated.
*Also check in the system logs for event ID if any error's are listed to check for error's listed when the system freezes.
I hope this helps ,if there are any concerns then do reply to this post with the service tag of the system sent via private message.