Looking at Setupact.log and Setupapi.dev.log

Setupact.log and Setupapi.dev.log are perhaps the two most important log files that are used during update/setup failure troubleshooting. Here are the locations these files will be typically located at, depending on the deployment phase:

• Down-level (Setupact.log): Used for troubleshooting rollbacks and down-level failures

Location: $Windows.~BTSourcesPanther

• Rollback (Setupact.log): Used to troubleshoot rollback and and uninstall failures

Location: $Windows.~BTSourcesRollback

• Windeploy and OOBE (Setupact.log): Used to troubleshoot failures during OOBE

Location: $Windows.~BTSourcesPantherUnattendGC

• Pre-initialization (Setupact.log): Used to troubleshoot pre-launch failures

Location: Windows

• Upgrade Complete (Setupact.log): Used for post-upgrade investigations

Location: WindowsPanther