Randomly disconnect from network, bandwidth below normal?

Just recently, my computer's started acting up. At random points, it will disconnect from my home network for no reason. If I try to reconnect, it tells me "Cannot connect to [network name]." Troubleshooting says that it's trouble with the router, but of my three other computers, all access the network fine, don't disconnect, and have normal speeds.

My download speed on the wireless network generally fluctuates between 8 and 12 Mbps download. On this computer, it now fluctuates between .62 and 1.93 Mbps. Other computers on the network are still getting the normal speed.

I haven't downloaded any suspicious files lately, and I've run virus scans (with Norton Security Suite 10), which came up clean. I've deleted all programs that I've installed since the problem started, and that had no effect. Task Manager shows no random peaks of network usage - even when the test shows a low speed, TM shows the network is wide open.

Running Windows 7 on an i7 720, 8GB RAM, 1TB hard drive.

Right now, I'm basically at a loss to explain why this is happening, so I'm just looking for suggestions as to what I should try next. Any help is appreciated. :)