XP prompts for an SP3 patch update, but prompts "Access denied" when installation is about to complete, and then the system automatically rolls back to its pre-installation state.

After working on it for most of a day, I finally found a method on the Internet that was effective after using it.

Specific methods:
1. Download attachment:xpsp3isOK.rar(136883 Byte);
2. Install subinacl.msi to the Program files directory of the system disk;
3. Execute reset.cmd (it takes a long time, please wait patiently);
4. Just reinstall SP3.

When installing XP SP3, it is recommended to temporarily turn off the monitoring and proactive defense of antivirus software. But make sure the computer is non-toxic first.

In addition, after installing XP SP3, more fragments are usually generated, so it is recommended to defragment them after installation is complete.