It is a log file that chkdsk creates as it is running. It is usually merged into the event viewer log, but if chkdsk were interrupted, it may have been left behind and/ or corrupted. You may be able to double click it to read it.
This could mean there are problems with the "disk" and the files have been lost. You could try running chkdsk again, but you may want to first try some recovery applications to see if they can find your files:
Free recovery applications:
1 - Recover Files
2 - Recuva
3 - Restoration