These are some suggestions that I offered up when one is having WiFi problems in their home.

1.  Location of the router in relation to the wireless computers.  It might be that something is causing interference or the location of the router is too far from the laptop.  Wireless routers give off a signal in a doughnut shape from it’s antennas.  This means that you could possibly be directly above the router and not be able to receive a signal.  Wire mesh inside of walls and brick will also decrease the signal.   You probably want to try and keep the router as centralized as possible if you want coverage throughout the house.  You can do this by just moving the DSL Modem that is connected to the router along with it to another telephone jack.  I know my parents don’t have that option but that is a rarity.
2. Static on the line. If you have DSL, make sure to have the adapter that the phone company gave you is between the DSL Modem and the wall.  This will help reduce static.  However, the static could be originating from the telephone box on the outside of the house in which case the phone company would have to come out and test it.  This works the same way for cable.  A weak signal will cause intermittent drops.
3.  Wireless card drivers need updating.  While rare, you should make sure you are running the latest drivers.  You can find that out by going to the manufacturer’s website and comparing the dates of the drivers to the dates on their website.

I’ve personally had all these issues at one time.  Always go into your troubleshooting with a plan.  Don’t take anything for granted.