I have about 200 Mathcad files / All of a sudden they all disappear. I did not delete them, where can they go?? how can I recover them?
I suppose you know the (path/directory) location where they should be.
If you use windows's File Explorer, check the files ((if any) that are in that location.
What did you do between having those files and not having them anymore?
Did you change from Mathcad Prime to Mathcad (version 15 or less), then realise that Mathcad does not deal with the .mcdx extension that Prime uses.
So far Mathcad (nor Mathcad Prime) is known for deleting files, although cases are known where Prime files are mutiliated such that they become empty.
According to the eleventh commandment "You shall make backups", you should have a backup.
To get the files back (if you really lost them), retreive them from the last backup that you made of your files...
These are things that happen when you have a "very bad" virus, or you have deleted the folder inadvertently.
it is always good to have a separate backup drive or make frequent copies of the work done, on usb drives.
However if you haven't formatted your hard disk, you could use one of those utilities that allow access to all files
on the disk (norton utilities) and then with great patience select and copy the files that interest.
In any case wait for the advice of other expert .
it may be that you have inadvertently moved the folder to another folder.
Sometimes it seems that the mouse is hooked to some folder, as you scroll through the tree, and paste it elsewhere .
Have you made the search for a lost worksheet that you remember the name?
Mathcad cannot delete files. You have either lost them or deleted them by mistake, or something else (probably nasty malware) has deleted them. As others have already said, your last backup may be the best solution. If you don't have any backups, and the files are really gone from your PC, you will have to treat this as your painful lesson about why you should have backups. Sorry.