[ubuntu] Impossibly slow install

I installed 16.04 on my desktop a few weeks ago. I broke it tweaking different desktops. Then I fixed it using the original installation USB drive.

This moing my computer would not boot from the HD so I again tried to repair it with the installation USB drive. However it seemed to freeze part way through the process.

After trying several times I then tried the nuclear option of another fresh install. Same result.

Each time I booted from the same USB drive.

So I thought that my installation USB must have become corrupted. I downloaded another ISO and a fresh USB stick. Same result, except that I opened the log screen and found that it seems to be taking a 6 minute pause after every few steps.

So far it has taken nearly two hours!

Is there anything that can be done?