Strange problem with router Belkin

It almost seems like there is some kind of throttling mechanism or bandwidth cap in the router. Try looking around in the settings for anything that will limit transfer speeds.

I'd also remove/reinstall any software that came bundled with the router to see if that eliminates the problem.

Let me put my thinking cap on ....... :> )

Has there been any changes to the configurations of the PC's connected to the router?

I didn't read whether you were connected direct or through a wireless connection to the router. There are some settings that will cause this to happen based on location of the router and wireless settings.

Are the speeds the same all the time or do they go up and down based on time of day? I had cable internet at one time and dropped it because I was experiencing the same problems as stated. Depending on when I tried to use the internet, I had good connections one time and lousy the next. They were having a balancing issue with our node. Also, they put too many folks on the node so upload speeds decreased dramatically. This made my connection speeds drop as the PC had to wait for a reply from the network before it could download or upload data. This is a latency issue.

Try pinging the router? EX: ping 192.168.1.1
The results should be short ping times, IF not you may have a cable problem. They can cause intermittent problems.

You may want to do a trace route on say yahoo to see how many hops and if there are any problems with the ISP routing. You will be able to see the results of your local ISP internal routings this way.

There are some throttling options on high end routers however, I've not come across them in most routers used for home applications.

I believe I gave you a lot to digest. There are a ton of things that can be tried. However, we need to limit the search. To narrow the field I recommend the above as a place to start.

I hope this helps ....:> )