Please consider the following setup:
A computer running a non-deprecated and up-to-date version of Windows (e.g. 7/8/10) is physically connected to a LAN or WAN network by means of a plugged-in network cable. The network adapter for this particular physical connection has been deactivated in Windows's Control Panel.
Wireless functionality, if installed in the computer, has been turned off on a low level (e.g. in BIOS/UEFI). Sharing and Remote Desktop functionality have been turned off, too. The Windows firewall is enabled. Default Internet Options are applied. There is no other security-related software installed.
Windows is idling. Sleep mode and hibernation have been turned off. No additional devices are or have ever been plugged in the computer (not including inconspicuous KVM) nor have there been done any changes to the software apart from installing the latest OS updates and original computer drivers downloaded from the Internet which was the only occasion of ever having been connected to a network before. (Power and physical access is not a concern. Sensitive data of any security level is or was never present.)
How difficult is it and by what means is or would it be possible to access such a computer from LAN or WAN and conversely, how "secure" is this setup?
Thanks for your input!