z, my guesstimation would be one of two things.
you might not be connecting to your own router. sometimes, your system connects to another router in the area, even though it's telling you that you are connected to your own. then, the other router kicks you out occasionally, especially under heavier use. try going into your system tray icon for the wireless router configs, and reconnecting manually to your router. if that works, try to see if there's a setting for default router, or being able to connect to only 1 router.
you might have to uninstall/reinstall the software on your computer and/or set up the security on your router again.
the other thing might be interference, but that would depend on something transmitting a fairly strong signal in your area.
hth.