Internet issue.Follow

Since last week, or about that, my internet speed has crashed down...
I used this test before and when I did it again today my download speed was down to a 4th of what it was while my upload speed remained normal.
50kB/s down and 25-30kB/s up before, 12kB/s down now.
(and yes, it wasn't much to start with but there's really nothing left now...)

I've tried to remember if anything happened to my modem/PC/software in the past week that could have affected it but I can't remember anything.
I called my internet provider but they say there's no issue and refuse to even say anything but that.


My pc specs, if that's of any help:
intel E6550 2.33Ghz dual core
2GB ram (ddr2)
Point of View 8600GTS 256mb video card.

I have no clue in which direction to search for the issue, so any help is appreciated.
Thanks in advance,
- Aethien