Raspberry Pi connects to WIFI but not to ethernet

Hi,

my Kodi 14.1 was running smoothly but was switched off some days.
When booting up again it didn’t connect to my network by ethernet (cable).
I had to plug in a WIFI connector to get access to the device.

Do you have any ideas why I can access only by WIFI and not by cable?
Is there any possibiliy to check log files etc.?

Thank for you help,
Sebastian