I didn'n have a login account on the computer before,but I synchronized a new account later,and all the original data disappeared,how can I restore it to the original state?
If you didn't have an account, setting up syncing would never have caused you to lose data.
If you had previously synced with a different account, when you switched the account set up for syncing, Zotero warned you that it would delete all local data for the old account, required you to check a checkbox saying "Remove all data for “[old account]” from this computer", and said to make sure you either had uploaded any data to the old account before continuing or had a backup of your Zotero data directory. Assuming one of those is the case, you can restore by either switching back to the old account or restoring from the backup.
Upgrade Storage
If you had previously synced with a different account, when you switched the account set up for syncing, Zotero warned you that it would delete all local data for the old account, required you to check a checkbox saying "Remove all data for “[old account]” from this computer", and said to make sure you either had uploaded any data to the old account before continuing or had a backup of your Zotero data directory. Assuming one of those is the case, you can restore by either switching back to the old account or restoring from the backup.