I have only used internet explorer as my browser so I will now try the others.
With regard to my anti virus— like an idiot, I didn’t just turn it off, I uninstalled it.
Most antivirus can't be completely uninstalled through Add/Remove Programs.
You have to also run an uninstaller utility that you download from the antivirus program's website. This utility cleans up files and settings that the normal Windows uninstaller leaves behind. So if you didn't use the antivirus' uninstall utility, the uninstalled parts of the antivirus may still be preventing downloads.
To find the uninstaller for your particular antivirus, do a web search for the name of the antivirus and the word "uninstaller." Since you never told us what antivirus you were using we can't find a link to its uninstaller utility for you.
If you are going to switch from your old antivirus to Windows Defender, you need to get rid of any leftover traces of the old antivirus. You also need to update Windows Defender with the latest signatures/definitions before running a scan or it won't be able to detect new virus.
If your old antivirus was McAfee, you are better off using Windows Defender.
McAfee is known for false positives.
Here's a website that tells how to get rid of McAfeehttp://www.pchell.com/virus/uninstallmcafee.shtml
This is just an example of what you may need to do to get rid of the last vestiges of an uninstalled antivirus. We have no idea if your old antivirus was McAfee or not.
If the problem with downloading is a problem with bad settings, then a system restore can help.
If you have a virus, then a system restore will not get rid of it.