What OS are you using?
How big is the drive to begin with? With modern operating systems you should have at least 15%, and some say 20 - 25 %, of the total drive space free at all times. This is more important with Mac OS X on Mac notebooks but also holds true for Windows.
Windows 10. THe drive is 111 GB in total, and atm I have 31GB free space.
I still need help.
What exact version of LR are you running?
Try opening a recent backed up catalog and test. If you are using LR 6/2015 the backups are compressed in ZIP format and need to be expanded before they will open in LR. If LR 5 or before then you can open them directly in LR, they are just full backups of the catalog file.
I'm using the latest version.
This backup you are refering to, will it contain my latest edits etc?
And where to find it?