Wireless connection problems

I connected the Mac using wireless with Talk Talk in 10 mins but cannot connect the HP Pavillion 430 desktop using wireless. Bought a Belkin wireless usb adapter but even tho the signal was good & it said there was a connection it wouldn't connect to the internet. Was advised to change this to a Netgear usb adapter today - again receiving 100% signal & being told there is connection but I still can't connect to the internet. Can anyone help please as this is driving me mad?