would suggest you to launch Lightroom with Control key pressed and choose the option to create a new catalog for test purposes and check if you are able to load new catalog.
If yes, go to File > Open Catalog > choose your main catalog to be opened.
What is the location of your main catalog?
Is it stored on the external drive or your local drive?
After several attempts and reboots I got it working again on the laptop, but it is version 6.1.1 because it has never been updated, I only use it on holidays usually.
Different story with the PC, it was 6.3. I tried holding down Control but it made no difference spinning wheel, then nothing.
I tried to reinstall 6.1 but I get an error message about machine needing a restart - every time.
I then tried to install my original 3.6 and it seems to work but says the catalog is too new.
Now trying to install 6.1 by ignoring the error message, it started the install, then I turned to write this and the the application manager window has partly opened and then just stopped. I cannot even close it so another reboot is on the cards.
To answer your last question, all my catalogs are an the local drive, in the "pictures" folder.
Thanks for the update.
You can update to Lightroom 6.3 on your laptop using this link : Keeping Lightroom Up-to-Date
On your PC, quit the task for Lightroom from task manager and go to Pictures folder> look for the main 2016 catalog and launch it directly from there > if it does not load, quit and test with 2015 catalog to confirm if its happening with a particular catalog.
Those created with LR3 open LR3 now that it is installed.
Those created in LR 5 do nothing, although the task manager says Lightroom is running but it never opens on the screen.
In addition, after 2 hours the LR6 started to install but all screens have frozen. I notice that the Adobe Application manager is 32 bit but my PC is 64 bit.
I did try a system restore but it said there are no restore points so those I created have all disappeared.
Strange that only lightroom and Application Manager are affected.
Everything else on the PC seems to be working normally. It as been running very well since I cleared out 1TB of pictures, as I do every year.
I would suggest to restart machine and update Lightroom first.
Then, you should manually open the catalog from your Pictures folder as I suggested and it would directly open in Lightroom 6.
It is the same as opening from the program icon, I use open with and select Lightroom (6) while monitoring the Task Manager, all it does is open the Adobe Licence utility and then everything stops, forever.
I have now also run the licence utility, the only change after running it is that lightroom opens momentarily in the task manager, then between 1 and 15 second it closes and the licence utility opens, then nothing more happens.
I have also re-installed the Adobe Application Manager and it still takes hours to do anything.
I have sent you a PM for further assistance.
Problem has been solved. Disc scan in safe mode unearthed an unrepairable corrupted windows file. Restored (reset) PC from initial back-up discs and restored all data from hard disc back-up. Fingers crossed, all will be well now.