Can you give us some relevant details about what is happening, and what error message (if any) you are seeing? Go ahead, be verbose, give us a very detailed explanation. Leave nothing out.
a few weeks ago - my LR5.7 would start taking forever to recognize the SD card and download the pictures.
Yesterday - it quit opening at all.
So I replaced a dll file that I saw on one of the blogs.
Still not opening.
So today I contact customer support via phone and they throw me into chat.
I've been in chat with a guy for over two hours - waiting for the software to uninstall (his suggestion) and re-install.
He's tired of me now, so here is my current situation.
The software seems to "hang" during install now.
You might look at what processes are going on.
It may be that Adobe LR is hung on opening so that it shows in the 'processes' but doesn't work.
In that situation it blocks further instances of LR.
It help if you say what operating system you are using.
Oh - sorry - I have Windows 8. I checked the processes - there should be no reason it doesn't install. I'll try rebooting and re-installing and see if that works.