Internet Speed Dropping After 3-4 Hours (Need help!)

I'm currently having major problems with my internet connection. I use a Linksys Wireless-B Internet Adapter to connect to a Linksys Router that's in my house, and after about 3-4 hours of internet use my speed goes from 3mbps to 0.50mbps. What could be responsible for this drop'age? Could it be the wireless adapter I'm using, or is it the router?

After it drops to 0.50mbps, I have to reset my connection in order to get it to go back to 3mbps. I have go to http://192.162.1.1 and change the channel.

Any help would be great, thanks.