Great thanks guys for the quick replies!

Hello,
I still have v0.11.1 running on my PC, and the application gets stuck on the "activating best chain" message, or it loads completely and then waits because "no block source available".
I think(!) I was able to make a backup of my wallet yesterday when it said "no block source available".

If I download the latest version of the bitcoin core client, can I just install this without deinstalling the previous version first?
There are coins in my wallet at the moment.

Any advice is appreciated!