download large file using browser fails before end

There definitely seems to be some sort of problem going on over the past few days with file transfers through the browser.  For several days, I haven't been able to upload any file larger than 1MB to my online folders, either through the advanced uploader or the basic uploader.  I very much doubt that it's an issue with my computer -- I have exactly the same internet speed now that I had in the past when Dropbox last performed as it should, I haven't noticed similar problems with other websites (since I'm able to download files from other sites), and I've performed a thorough tune-up on my computer (updated the operating system, updated the anti-virus software, scanned the computer for malware, cleared out the junk files, removed obsolete entries from the registry, defragmented the hard drive, etc.). I've submitted a help desk ticket to Dropbox but haven't heard back from anyone yet.

When I try to upload a file larger than 1MB, everything is fine for a couple of moments and the file seems to be uploading at a reasonable speed, but before it can finish uploading, the progress bar suddenly goes back to a much earlier period and the upload speed drops way down to the point that it initially says even a file just over 1MB will need more than ten minutes to upload (which is crazy, since that implies the upload speed has decreased to just bits rather than bytes per second).  After a couple of rounds of this, the updater quits and gives me an error message saying "something went wrong with the advanced uploader" (no...really???).  The basic uploader is no better -- it says that it's uploading the file but never finishes.  It's ridiculous for Dropbox to need more than half an hour to upload a file of only 1.5MB...even a dial-up could do better than that.