My problem is that I cannot make e-mail attachments or upload images to sites like tumblr or deviant art. In some cases I get an error message like UNKNOWN ERROR but mostly they just never finish loading (even after 5 minutes of waiting). This happens in Chrome, Firefox and Vivaldi and in incognito mode. I restarted the computer, emptied the cache, etc. from all three browsers and reinstalled and updated Firefox and Vivaldi with no help. Yesterday everything worked fine, the computer slept overnight, and this morning I could not upload or make attachments. I did not install any software or apps. There does not appear to be any other issues. I am using Windows 10.