Airport Wireless Internet Not Working on iBook G4 - Airport

Hi,

I've been having a problem with my iBook G4 for the past few months. First, every time I was using my wireless internet, my browser kept freezing, and I was forced to restart my computer each time. And almost every time it loaded back up again, my Airport symbol would disappear for few hours or a day and I wouldn't be able to connect to the Internet. After going to a Mac service centre a couple times, they recommended I wipe everything out and reinstall from scratch. I've done that plus the updates, and everything is working perfectly, except for my wireless Internet. When I connect using a cable, no problem - surfing online works great. But when I try to search for a network at my place or my friend's place, the Airport icon is gone, and it says Airport is turned off. It also says 'No Hardware detected' but my iPod Touch and all my friends' lap tops can connect no problem. I went back to the Mac service centre, and as soon as I booted it up a signal came up immediately. When I surfed the Internet, it worked like a dream but as soon as I returned to my friend's house and then my place, my wireless won't work! I think I have a bad case of Mac Voodoo! Does anyone have any suggestions?

I'm thinking the Airport card in the motherboard is faulty, or it works on and off - but I don't know whether it's worth replacing. Any help would be much appreciated!!

Thanks,
Kimiko