A registry tweak on Windows 2000 Server (TCPWindowSize added; a key removed) causes the system to hang before logon. Which recovery option safely restores the previous working control set?

Introduction / Context:
Windows 2000 maintains multiple registry control sets and records the last configuration that successfully reached the logon screen. If an update to system settings (including registry edits that affect drivers/services or networking) prevents a successful boot, using Last Known Good Configuration can revert to the previously working ControlSet quickly without manual registry surgery.

Given Data / Assumptions:

• Registry was edited (TCPWindowSize added; an unused key removed).
• System now hangs before the logon UI appears.
• No file system damage is indicated; the problem is configuration-based.

Concept / Approach:
LKGC restores the ControlSet that was active on the last successful logon. Because the failure occurs before logon, LKGC still points to the earlier, good configuration and will overwrite the current failed ControlSet with that known-good one. This is faster and safer than Recovery Console for registry-level mistakes.

Step-by-Step Solution:

Verification / Alternative check:
Confirm the system reaches the logon screen and services load normally. Review System event logs for driver/service issues tied to the prior edit.

Why Other Options Are Wrong:

• Safe Mode still uses the current ControlSet and may not undo a bad registry change.
• FIXBOOT repairs boot sectors, unrelated to registry configuration errors.
• Changing winlogon service state is irrelevant and risky.

Common Pitfalls:
Booting once successfully (even briefly) after the bad change will update LKGC; use it immediately after failure.

Final Answer:
Boot using Last Known Good Configuration (LKGC)