Completed downloads freeze Windows
There are several ways Antivirus software may be scanning the file.
- When it hits the disk, if the file is compressed scanning can take some time and cause a pause/hang.
- Intercepting the web request and scanning the file before allowing it to complete. Will usually see items for the security software listed in the network connection properties.
- A helper addon for the browser that scans the file before allowing the transfer to fully complete.
Turn off various scanning features, download the EICAR.COM test file from someplace to confirm then see if the hangs go away on larger files.
FWIW I get the same problem randomly. I see the 99.9999% green progress circle just sitting there. It could be a tiny file and it will just sit there freeze my entire OS until the green circle completes. Sometimes up to 5 minutes or more.
I don't know if it's AV related although I suspect it might be. I use F-Prot and MSE here. Maybe it's the combo?
You mention switching anti-viruses, but nothing about disabling them. Granted, switching that many times would probably rule out AV but I'd simply disable whatever you have running. That or uninstall something like Dropbox, just to rule it out. Also, AFAIK Malwarebytes isn't a full blown AV software. It shouldn't be run on its own. Even today, I've had issues with Malwarebytes Anti-Exploit preventing IE, Word, Excel, and Powerpoint 2010 from starting.
I'd also check Task Scheduler and MSCONFIG for any startup entries, as well as Services(.msc). Look for anything that isn't critical and disable it. Restart and see if you can work normally.
Although I can't think of anything specific, Windows Updates may cause bizarre issues. I'd check to see if any Windows Updates could cause the issue described here.
Since it affects so many different areas, I'd think it's a virus or hardware that is failing. I'd run Memtest and manufacturer diagnostics on the drives. After that, I'd do an offline virus scan (Kaspersky has always done well for me).
If nothing else, reinstall Windows. Perhaps a slightly better method would be to dual boot and see if a fresh copy of Windows functions normally, so that in the event it doesn't you can switch back to your old copy. If a clean install didn't work, I'd say hardware failure or a bad copy of Windows. If you're using a pirated/illegal copy of Windows, you should absolutely expect problems.