Are you using LR6.6, the latest version?
Are you on Mac or Windows?
Where are the RAW files located - internal drive or external?
Do you export to the internal drive or external?
To build on F. McLion's query, please do Help > System Info and report the exact version of LR you are running and which version of Windows or Mac. LR CC 2015.0 / 6.0 introduced a serious bug that caused the symptoms you're reporting, but it was fixed a year ago in 2015.1.1 / 6.1.1.
im using Lightroom 6, it was bought in December, so don't know if that is the latest version.
im on windows 7.
raw files are saved on internal HD
export to internal HD.
What is this download for?
will I lose my Lightroom work?