is you operating system 64bit or a 32bit version perhaps

64bit as stated above

Did you try running the installer as an administrator (from right-click menu)?

Run as administrator tried and failed

More info.

Downloaded several more earlier .EXE files and all reported You need WIN7 or later.

Howver I stated in post #1 ...tried earlier versions 78.10.2 and 72.0b3 with same result, and the .msi versions which just fails but reports nothing.

I have now discovered that 72.0b3.msi did actually install. Just tried it again. The problem is that there is no on-screen activity, e.g. Do you want to do this - Where do you want to put it - Installation complete, etc

It just stuffs it in C:\Program Files (which is the last place I wanted it). You later find a new icon has mysteriously appeared on the desktop.

So - bottom line is still something wrong with the .EXEs, and the .MSI version is really unfit for purpose. Further investigation necessary! However I do now have a working Thunderbird running on WIN10 Pro 64bit. That must be progress after about eight hours p*ss*ng into the wind. Everything was / is so much simpler with WIN XP. The quality of software has seriously declined since then.

I rather doubt there is anything wrong with the installers from thunderbird.net, otherwise there would be many complaints, but possibly some 3rd-party app on your computer is blocking the install. Try running W10 in safe mode to bypass startup apps and then see if the TB installers work.

Ran WIN10 in Safe Mode with 'Minimal' selected.

Still insists I need WIN 7 or later.

I have installed very little on this new PC. Only mods have been to remove much of the Microsoft garbage.

Guess I should add I became a software engineer in 1982. Recently retired - a welcome experience looking at the mess that abounds today.

Only mods have been to remove much of the Microsoft garbage.

What you removed probably included parts that explain your issue. Try it with a fresh install of W10 and no mods.

I have had no troubles installing Thunderbird on Windows 10. I have had upgrade issues but no install issues. That would indicate to me your windows install is broken.

A common misconception is that you can use symlinks to redirect a lot of windows default file and folder locations. While this is technically possible an unstable windows install is usually the result and is not supported by Microsoft.

BTW I would suggest that "I have a very new PC running WIN10 Pro 64bit ver 21H1. Have downloaded the latest recent version: 78.12.0" is quite deceptive really as your windows install is modified by your own later statement. Install Windows, install Thunderbird and if there is a problem then we have a base line to work from.

I think this thread has hit a brick wall. Let me summarise the FACTS:

1) Don't know anything about symlinks. The only un-installs I have performed have been via Programs and Features relating to Cortana, Office and a several other MS items of which I have no need.

2) Winver tells me I'm running Windows 10 and that's good enough for me. It is also good enough for all the other applications I've added. I have had no other installation issues and have added five more apps since the start of this thread.

3) As reported. the .MSI version installed Thunderbird on my PC and it works fine - hence there is nothing wrong with my Windows as-is. I DO NOT NEED TO REINSTALL WINDOWS. As a test I tried the .msi on WIN XP and it correctly reported the incompatibility.

4) The message generated by the .EXE you need WIN7 or later is, like so many error messages, clearly flawed. It is a perfect example of a Microsoft-style error message in that it is factually 100% correct, but of no use whatsoever to man nor beast.

Conclusion there is something wrong with the algorithm used by the EXE files in determining the OS. Let's leave it there - with luck it will go away

Consider using Thunderbird as ready2run. I never need to install and run from a USB if I chose.

The MSI has no user interface to customize the install. That is the only difference. The only other issue may be how your anti virus handles self extracting Zip files which is what the installer is. Otherwise I have installed recent versions on windows 10 and I have had no errors. So unless you want to start comparing what you have V what I have there is nothing to say but there is a problem with your install.

My personal feeling is you will find you have set some security level to high in some component like your anti virus. But it is just a guess as I really know nothing about your issue as I can not reproduce it.