X1 Carbon Gen 3 - turns on but no display, no error code, no beep.

Hi @karunanitheem

"....throwing CMOS battery error message..." is the clue.

The laptop has a coin cell cmos battery connected to the motherboard which is used to maintain the BIOS settings when the laptop is turned off.

This is a non rechargeable battery so when the battery voltage drops from the normal 3V to below approx 2.4V the BIOS can become corrupted which can prevent the laptop from starting.

You are unlucky as the battery is connected on the underside of the motherboard, so to replace it, the motherboard has to be removed from the base assembly.

Here's the hardware maintenance manual for the laptop.

Go to p.69 (75 of 98 pdf) in the manual to view the procedure to remove the systemboard and then the coin cell battery.

Search online for 00HN933 to find suppliers that suit you best.

Once the battery has been replaced and the laptop reassembled, when you start the laptop (if it turns on) there may be a message stating that the date and time are incorrect. This is normal as the BIOS has been reset back to its factory default state by the disconnection of the cmos battery during the replacement procedure. Once the date and time have been corrected, the message won't appear the next time the laptop is turned on. Also any user definable BIOS settings that were changed by you, to suit whatever system requirements you wanted, will have to be changed back again as well.