I have Windows 7 x64 on my Dell laptop.
I've got LR 5.7 and CC 2014 and yet they are successfully associated with CC 2014.
You can try going through the Control Panel
All control Panel Options > Default Programs > Associate a File Type with a Program
Let the list load up, select the Extension, click on the Change Program button, and if it's not listed, browse for it.
Hopefully you can add and select it.