Is it possible that there's interference? Microwaves? Cordeless
phones? Another wireless device nearby?
If not, then I suppose it's time to start swapping things out on a
larger scale.
Try a different wireless adapter on your laptop. Get a cheap usb
adapter and install it. See if you still have the same problem.
If the substitute adapter works, then it's in the laptop's built-in
adapter (+installation+settings).
If it's still the same problem, then test another laptop/pc with the
same router and same adapter. If that works, then it's in the OS on
the laptop....