help please

Hi,
I am trying to set up a wireless network in my house to connect my sons
notebook to the home pc
That's the easy part......then it all goes like this,
I can network with other pcs and when I took my sons notebook back to the
shop the techie (sic) managed to tewak it and get it to connect to the
internet so we thought .,ok, this is right .
When we got back home...............
NO SIGNAL surprise ,surprise and the notebook keeps dropping the signal
after 2-3 seconds
The card works in 2 other notebooks
Identical settings used
Same O/S
Is anyone out there able to shed a load of light on this please
a stressed Jude




jood