This can happen if the windows list separator (under control panel|regional
settings) doesn't match the separator used in the .CSV file.
For instance, with my USA settings, my windows list separator is a comma (,).
If I import a file that uses a semicolon (

as its separator, then all the data
goes into a single column.
I can either change my windows list separator (temporarily) and then reimport
the .CSV file. Or I can select column A and do data|Text to columns and specify
the matching separator there.