Can you tell us from the start what happened please.
What do you mean by "lost part of several files" how can you lose part of a file?
What are the file types you lost? (if excel then they would be .xls file type)
How did you lose them (What happened to make them lost)?
How did you manage to recover them? and what file type are they?
What program are you opening them in to discover they are ASCII symbols?
If you give us as many details as possible we may be able to help.