Hi,
When an import fails it will give you the option to download a log file, if you open it in Excel the second tab will show the error status against individual components.
The processed one are which had no issues during import. When there is any error with any component, then all the componenets after that shows up as unprocessed. You should be able to find the error next to the component because of which the import failed.
Check for the component with "Failed" status. Besides the status, you will also see the error message and error code. If you could find that error and paste it here, it would be easy for us to solve your issue.
Common reasons can be:-
Addition field in the target environment
Data Type Change of any attribute etc..
Else the last option would be to enable trace. In the trace logs you will definately find the error.
Hope this helps!!!
Thanks,
Prasad
Make sure to "Vote as Helpful" and "Mark As Answer",if you get answer of your question.