Dropped Wireless Connection on Laptop

Okay, here's the situation. I have here a laptop - emachine E529-2417 with intel Celeron P4600, intel HD graphics, 2 GB DDR3 memory, 320 GB HDD, 802.11 b/g/n. The network adaptor is Atheros AR5B95 Wireless network adaptor. It runs Windows 7 64 bit. I have Rogers Cable high speed internet using a Cisco router. I have no problem with the internet on my desk top computer and Craig doesn't have a problem on his laptop. However, Sarah's laptop, the aforementioned emachine, keeps dropping the internet every 5 minutes (slightly exaggerated but not by much). I've scanned, deleted and all that I know how to do. I also removed the driver for the wireless on the problem laptop, then re-installed and update the driver from emachine's website. At the same time, I removed the saved wireless connection and re-create the profile from scratch. She has Norton 360 as her antivirus program. Any suggestions on what could be the problem?