With limited detail to go on the chances are that your catalogues were locked. They could have been unlocked by deleting the lock file. See here for its location (it's for LR5, but it's still valid):
The crashing could have been the result of GPU acceleration. See here to turn it off.
Also it's not really Windows 10: it's Technical Review so chances are it's not really stable enough......
Various reports in this forum indicate that the public release LR6 is not quite ready for Win10, especially since win10 is not released yet.
It is safe to assume that Adobe is working on it in their labs, but Adobe is not talking to the public about it.
I hope this issue will be resolved soon after official release of Windows 10, till now I'm not able to use LR at all due to sudden crashes.
PS: I've already checked locked fil. It does not help.
So we shall wait!
Do you have any news concerning compatibility between Windows 10 and final release of LR?
Some people report problems, other are running just fine.
Your posts contain on description of the problem(s) you are having, which makes it difficult to help you.