Belkin Routers :: N150 Fast Wired / Ultra Slow Wireless

I bought my own modem, a Motorolla Extreme something or other, is a DOCSIS 3.0. My router is a Belkin N150. When I plug my desktop computer directly into the router, I get speeds upwards of 50Mbps. The wireless, however, gets about 0.15Mbps download, but as much as 12Mbps upload.

I know it's not computer specific, because I plugged my laptop directly into the modem and got the full speed. AND I put a wireless adaptor on the desktop and got the slower speeds.I live in a densely populated area and there are 27 other (visible) wireless networks available (all locked, unfortunately. Otherwise I wouldn't be in this situation in the first place). So I tried every channel, doing a speedtest with each, and I got almost identical results each time: 0.12-0.17Mbps download, 11-13Mbps upload. I can't imagine that getting only 0.15Mbps could be a result of a channel being clogged, but I tried it anyway;