If Google Sheets will not open, first separate a single-file problem from an application-wide loading problem. An access-denied message, an editor error, and a lost connection require different checks. Preserve any unsaved work before refreshing a file that is already open.
A spreadsheet can open without granting permission to edit it. Identify whether the whole file is view-only, particular cells are protected, or you are looking at an Office-format file through a different viewing mode.
A copy of a Google Sheets file is a separate working document. Use it for a controlled experiment or a new version, but do not confuse it with the original shared spreadsheet or assume it carries the same history and access settings.
A Sheets link can open under a different signed-in Google Account from the one the owner authorized. Resolve that identity mismatch before requesting new permissions or copying the file into a personal workspace.
Opening an Excel workbook in Google Sheets does not always convert it into a native Sheets file. Decide whether you intend to edit the original Office file or create a separate converted copy before making changes.
Moving an Excel workbook to Google Sheets requires more than confirming that the file opens. Preserve the original and compare the calculations, structure, and outputs that make the workbook useful before adopting the converted version.
A Google Sheets file can exceed a product limit or become difficult to use well before that limit. Check the current limit and workbook structure before deleting records that may be required for the task.
If Google Sheets cannot save changes, preserve the work still visible on the original device before refreshing or closing it. A saved-state warning concerns synchronization; it does not automatically mean the cloud file has been deleted.
Prepare computer offline access while you still have a reliable internet connection. A spreadsheet that opened online once is not automatically a verified offline copy, and offline availability is not a replacement for an appropriate backup.
If another device does not show your offline Sheets edits, return to the device and browser profile where you made them. The cloud version may simply not have received the changes yet. Do not erase the original local state while investigating.