I upgraded from Windows 10 to Windows 11 using the Installation Assistant and chose to keep my files. The first attempt failed during the restart with an "Undoing changes to your device" message. After running DISM RestoreHealth and System File Checker, I tried the upgrade again, and it completed successfully.
However, Windows 11 is now almost unusably slow. Settings, Steam, and my web browser take a long time to open, and even basic actions lag badly. Restarting and waiting did not help. I'm currently running sfc /scannow again, but it has been going for about an hour and is only at 33%, compared with roughly 15 minutes before the upgrade.
The computer still uses a roughly five-year-old hard drive containing important files, so I'm worried that the drive may be failing. What should I check first, and should I return to Windows 10 or move Windows to an SSD?
3 Answers
Before doing more repairs or another operating-system change, back up the important files immediately. A five-year-old hard drive could be slowing down because it is failing, and repeated scans or upgrades may put extra stress on it. Check the drive’s SMART health with a reputable diagnostic tool and look for errors in Event Viewer. Also confirm that the computer meets Windows 11’s requirements, especially TPM, Secure Boot, memory, and processor support.
The System File Checker result matters: “completed successfully” is not the same as finding and repairing corruption. Let the current scan finish once, but avoid repeatedly running DISM and SFC without a specific error to investigate. If the drive shows warnings, unusual noises, very high disk usage, or scans that take far longer than normal, prioritize copying your data and replacing the drive. If the hardware checks out, a clean Windows installation on an SSD is usually more reliable than trying to repair a badly degraded upgrade.
If Windows is installed on a mechanical hard drive, that is probably the biggest performance problem. Modern Windows can feel painfully slow on an HDD, especially after an upgrade while indexing, updating, or rebuilding caches. Installing Windows on an SSD—preferably an NVMe drive if the system supports it—should make startup and everyday use dramatically faster. Keep the old drive connected only after making a backup and checking its health.

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