TL;DR version: My download speed has decreased to about 1/40th of its previous speed, while my upload speed remains the same. Speedtest shows that my connection is equally strong as it was prior to the slowdown, even though I can't even get anything close to my original speed.
Fully detailed version: About a week ago, my download speed decreased from 2 megabytes/s to about 50 kb/s. Prior to the speed decrease, I did not install or update any programs, so it's probably not an interference from some wayward program. I've likewise not encountered any suspicious activity on the computer, nor have I visited suspicious sites, so it probably isn't a virus either.
There are several odd things, however. While my download speed has dropped so dramatically, my upload speed is exactly the same. According to a Speedtest.net check from August, my download speed was 8.5 mb/s and my upload speed was 4.14 mb/s. Currently, it is practically the same, at 4.09 mb/s. What is really strange, however, is that according to the Speedtest from today, my download speed is 9 mb/s, even though I can still not exceed 50 kb/s.
I tested IDM (download accelerator) on some of my skydrive files, since download accelerators allow for multiple streams of data simultaneously. I was able to download around 500 kb/s, which is still not even close to what I used to be able to reach from skydrive with IDM before (~2000 kb/s), but still much higher than if I only used one download stream (~50 kb/s).
Additional info: Browsing speed and video streaming is also much slower than usual.
Thus, I'm really confused. Does this seem like a problem of the ISP, or is it on my end? It seems as though even though my connection itself is strong as ever, my computer seemingly can't utilize the potential of that connection anymore.
Any help would be greatly appreciated. Thanks in advance!