Yes, my DELL OPITPLEX 755 stuck at 'Starting Windows' in early Novemebr 2017, probably after an update of AVG.
I searched the internet and tried many, many things. I was able to get the system to work, but as soon as I powered off the computer the same thing happened. I was able to keep the computer working by allowing it to sleep only, but not power off. Today, I finally managed to fix it permanently.
The reason that it stuck was that windows started successfully, but other essential programs had to be started before the Users ID screen appeared. However, it never got there because the anti-virus AVG was 'corrupted'. The following was what I did to fix the problem.
1. Power on your computer and keep hitting the F8 key.
2. Choose start in Safe Mode. I chose 'start in safe mode with networking'. Don't know whether it is essential to have 'with networking'.
3. Uninstall AVG. (I tried 'repair' when prompted, but the computer said it could not repair. it.)
4. Restart, and the computer should restart normally, passing through the 'Starting Windows', and ending in the users sign in page.
5. Sign into an Administrator account. Chances are, you are one if you end up in this blog.
6. The computer should now work. You can verify it by 'restarting' to make sure that it does not stick at 'Starting Windows'.
The computer will now gives you a warning that you do not have an anti-virus' program. Otherwise, it should be working normally. To fix the 'no anti virus program', I guess you can reinstall AVG, but I found that MS now provides a ''Microsoft security essentials' program. I did the following to add it as my default anti virus program.
7. Go to 'Control Panel' and navigate to 'Windows Update'. Click on 'Restore Hidden Updates"
8. Restore the update for 'Microsoft Security Essentials', and install it along with any other updates.
9. After installing and restarting, your.computer should be back to normal startup and functioning.
If the 'Microsoft Security Essentials' update is not available to you in your list of updates available or hidden updates, I suppose it is possible to request it through a web search. I have not tried it.
I spent many stressful days and nights trying many suggestions. The only one that helped was a blog where a responder asked whether the user on the verge of committing a self destruction was by any chance using AVG. I read that but unfortunately did not try to remove AVG until many more stressful days and nights. After I fixed the problem, I googled 'windows 7 stuck at starting windows avg', and ended up in this site among many others. The time stamp of the blog of early November 2017 was when I encountered the problem.