After giving this some more thought, doing a little research, and with the additional information you provided, here are a few things you might try. P.S.-I agree that this is probably not a hardware/AC adapter problem especially given the behavior of "info3" that you provided.

1. I found this at the Lenovo forum titled "X1 Carbon Won't Boot without AC Cord - reset switch" which states:

When servicing the system, or when storing it for an extended period of time, the battery can be electrically disconnected. There is an option in BIOS to disconnect the battery - AC must be unplugged while doing this step.

To start up the next time, attach AC and press the power button.

If the system become hung and will not power down, or will not start even with the AC connected, try using a paper clip to press the small reset button found inside a hole in the bottom of the system.

2. Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem. You sound very tech savvy so I won't bore you with the details on how to do it.

3. If that doesn't work, you might try doing a "Refresh" of Windows. Microsoft has instructions on how to do this on a Windows 8.1 system titled "How to refresh, reset, or restore your PC". Note: Doing this is pretty drastic however since it will remove any apps you've installed from the web (not the Microsoft Store...those will automatically be reinstalled) and from CD/DVD. If the laptop came with Windows 8 installed (has a "Recovery" partition with Windows 8), the laptop will revert to Windows 8 and you will need to manually update it again to Windows 8.1.

Note: This is too long for a 'Comment' so I posted it as an 'Answer' even though it's really just some suggestions.

After giving this some more thought, doing a little research, and with the additional information you provided, here are a few things you might try. P.S.-I agree that this is probably not a hardware/AC adapter problem especially given the behavior of "info3" that you provided.

1. I found this at the Lenovo forum titled "X1 Carbon Won't Boot without AC Cord - reset switch" which states:

When servicing the system, or when storing it for an extended period of time, the battery can be electrically disconnected. There is an option in BIOS to disconnect the battery - AC must be unplugged while doing this step.

To start up the next time, attach AC and press the power button.

If the system become hung and will not power down, or will not start even with the AC connected, try using a paper clip to press the small reset button found inside a hole in the bottom of the system.

2. Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem. You sound very tech savvy so I won't bore you with the details on how to do it.

3. If that doesn't work, you might try doing a "Refresh" of Windows. Microsoft has instructions on how to do this on a Windows 8.1 system titled "How to refresh, reset, or restore your PC". Note: Doing this is pretty drastic since it will remove any apps you've installed from the web (not the Microsoft Store...those will automatically be reinstalled) and from CD/DVD. If the laptop came with Windows 8 installed (has a "Recovery" partition with Windows 8), the laptop will revert to Windows 8 and you will need to manually update it again to Windows 8.1.

After giving this some more thought, doing a little research, and with the additional information you provided, here are a few things you might try. P.S.-I agree that this is probably not a hardware/AC adapter problem especially given the behavior of "info3" that you provided.

1. I found this at the Lenovo forum titled "X1 Carbon Won't Boot without AC Cord - reset switch" which states: When servicing the system, or when storing it for an extended period of time, the battery can be electrically disconnected. There is an option in BIOS to disconnect the battery - AC must be unplugged while doing this step.

To start up the next time, attach AC and press the power button.

If the system become hung and will not power down, or will not start even with the AC connected, try using a paper clip to press the small reset button found inside a hole in the bottom of the system.

2. Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem. You sound very tech savvy so I won't bore you with the details on how to do it.

3. If that doesn't work, you might try doing a "Refresh" of Windows. Microsoft has instructions on how to do this on a Windows 8.1 system titled "How to refresh, reset, or restore your PC". Note: Doing this is pretty drastic however since it will remove any apps you've installed from the web (not the Microsoft Store...those will automatically be reinstalled) and from CD/DVD. If the laptop came with Windows 8 installed (has a "Recovery" partition with Windows 8), the laptop will revert to Windows 8 and you will need to manually update it again to Windows 8.1.

After giving this some more thought, doing a little research, and with the additional information you provided, here are a few things you might try. P.S.-I agree that this is probably not a hardware/AC adapter problem especially given the behavior of "info3" that you provided.

1. I found this at the Lenovo forum titled "X1 Carbon Won't Boot without AC Cord - reset switch" which states:

When servicing the system, or when storing it for an extended period of time, the battery can be electrically disconnected. There is an option in BIOS to disconnect the battery - AC must be unplugged while doing this step.

To start up the next time, attach AC and press the power button.

If the system become hung and will not power down, or will not start even with the AC connected, try using a paper clip to press the small reset button found inside a hole in the bottom of the system.

2. Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem. You sound very tech savvy so I won't bore you with the details on how to do it.

3. If that doesn't work, you might try doing a "Refresh" of Windows. Microsoft has instructions on how to do this on a Windows 8.1 system titled "How to refresh, reset, or restore your PC". Note: Doing this is pretty drastic however since it will remove any apps you've installed from the web (not the Microsoft Store...those will automatically be reinstalled) and from CD/DVD. If the laptop came with Windows 8 installed (has a "Recovery" partition with Windows 8), the laptop will revert to Windows 8 and you will need to manually update it again to Windows 8.1.