Thanks Fihart. What the problem was is the old USB wifi reciever I was using didn't have a strong connection. I also have two routers, both on channel 6. I switched one of the routers to channel 8 so it wouldn't interfere because of the distance between my computer and the router is quite far.
Smart move to change channels. You might also consider this:
1) raise the router above furniture level
2) Experiment with channels (some will work better or worse depending on your environment)
3) If you can detect strong neighbouring wifi, use a channel 5 stops away from strongest.
4) Relocate cordless phone base or video sender etc.
5) Be prepared to move the computer (or at least turn it so your body is not between the router signal and the wireless adapter's antenna.