One of the most common reasons for Moneydance files seemingly being "lost" is that something has happened to your preferences file, i.e. it has been damaged or deleted, and hence Moneydance does not know what file was last used or where it is.
This problem is more annoying than anything else as it does not affect the data itself.
Search you machine for files that have the extension .moneydance (these are data files) and/or .moneydancearchive (these are your backups)
Maddy on 18 May, 2022 09:58 AM
In addition, if Moneydance is opening in the Welcome window and your data file/s are not listed on the right side of that window, you could click Open other and navigate to the location where your data is stored.
Another possibility, could be that you have accidentally launched an older version of Moneydance, perhaps?
Which version and build number do you see displayed?
(navigate to Window->Welcome to Moneydance)