Lenovo ThinkPad R400 7439 Hardware Maintenance Manual page 68

When you replace the system board, you must set the UUID on the new system
board as follows:
1. Install the ThinkPad Hardware Maintenance Diskette Version 1.73 or later, and
2. From the main menu, select 4. Assign UUID.
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ThinkPad T400 and R400 (14.1-inch widescreen) Hardware Maintenance Manual
restart the computer.
A new UUID is created and written. If a valid UUID already exists, it is not
overwritten.