Sorry, I may have misunderstood. Is the data missing from the PC rather than from the watch?
If it's the former, you may be lucky. Depends what you're downloading it to. If it's the Garmin software, you may find the data is archived, but I can't tell you anymore as I don't use it. If you changed your profile, it sounds like you need to change your profile back to what it was.
You can delete watch data by going to "History" where you'll find the option to delete all.