You did post this already but your screenshot this time makes it clear what the problem is. This is no bug, at least not a SketchUp bug. Lock works on groups and components. Your screenshot shows that you only have loose geometry selected. Create a group or component to contain the geometry and then you can lock it.

I expect there's a simple explanation for it. Share your SketchUp file so we can see what you are working with. Also please update your profile. It says you are using SketchUp 2014.

@onzki said: My user account is already set an admin level too when it was installed. That is not at all the same as right clicking on the downloaded installer and choosing Run as administrator. When you reinstall or repair the installation, use the right click/Run as administrator thing or you're just wasting your time.

Finally! It has taken me 24 hours of disabling and enabling everything I can, numerous restarts, cache clearances etc, and the thing that finally worked was to enable my VPN and set it to a US server, suddenly all my problems were solved! I've no idea why this worked but it did and I'm not going to question it in case I jinx it

Hi everyone, I have figured out the issue - I did run out of space and had to move files to another hard disk before I could continue working on my Sketchup model without moving the file. Thank you everyone for your help! L

Very likely the windows are opening off screen. First thing to try is Window>Preferences>Workspace and click on Reset Workspace.