Sounds like an OS and or hardware problem. Something is crashing LR.
Any idea of what it is or what I can do to fix it?
Start by running Memtest 86 and let it run overnight.
Then do some checking of your hard drive and update the video drivers (or downgrade them if for some reason they got updated automatically).
This is a problem I've often had with Photoshop.
If, as others here assume, you are running Lightroom in OS X, start with the basics. Use Disk Utility to repair the disk and repair permissions. Restart your Mac and try Lightroom again. If the crashing problem is not fixed, move your Lightroom preferences to the trash (don't empty it at this point). To locate LIghtroom's preferences (plist) files, in the Finder hold down the Option key and click on the Go menu; select Library; this will open the Library folder in your user folder (normally hidden in the Finder); open the Preferences folder and locate the com.adobe.Lightroom6.plist file. Once you've moved this to the trash, restart Lightroom and quit it once more. If LR continues to crash, move the com.adobe.Lightroom6.LSSharedFileList.plist file from the Preferences to the trash and test Lightroom again. If it continues to crash when you shut it down, you can return these two files to the Preferences folder as they are not causing the problem (Lightroom will have created new versions of these files. Move the new ones to the Desktop temporarily until you've put the old ones back. Then you can trash the new copies. You may have had to set some preferences after you removed the preferences files in order to get Lightroom to run properly. At a minimum you will probably have to locate your catalog file. Be sure to make note of the exact name and location of the file Lightroom is using, before removing the prefs, so you can find it again.)
If you are running Lightroom in Windows, you will need to wait for someone versed in that system to provide some help.
Be sure and let us know if any of these solutions works for you.
The problem is still not fixed. Thanks for all of your help anyway.