Are you signal strength and signal quality readings OK?
My brother experienced somthing similar. Turns out a neighbor set up a new router and was transmitting on the same channel and interfering, so we switched it to use channel 1 instead of 6.
Do a scan of your wifi environment and try to choose a clean channel. Channels 1, 6, and 11 are the three non-overlapping channels, so try to pick one of these.
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Also make sure you keep both the laptop and the router/AP away from any 2.4GHz interference sources, like microwave ovens and 2.4GHz cordless phones.
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