Answer first
Try opening a blank document, check Microsoft 365 sign-in and activation, test safe mode if available, disable recent add-ins, and use app repair before reinstalling.
If one file fails but a blank document opens, the issue may be the file. If all apps fail, review installation, activation, or account status.
A recent update or add-in can prevent launch. Note when the issue started and what changed.
Keep app name, subscription status, error message, device, and whether web versions work.
Quick FAQ
Why is Office not opening?
Common causes include activation prompts, update errors, add-ins, damaged files, account sign-in, or app installation problems.