ImacG5 won't cooperate with internet

I have an Imac G5 from 2005. When I was at my parent's house it couldn't find the wireless internet signal, and unfortuantely I can't remember how I finally connected it. I've moved into my own place but I'm visiting my parents on holiday for a while and I brought it with me. I can't get it connected and I need it for work. The Mac support hotline wouldn't help me and I'd have to wait to contact the internet provider. The computer can't find any signal at all and when I entered the information for the network (or what little I could find. Thanks Vista...) it still didn't connect. I even hauled it downstairs (my computer is on the second floor, the wireless base thing is in the basement), unplugged the port and hooked it directly; it found the network but still couldn't connect. Can someone tell me how my Mac can find the signal or whatever I can do? Help is much appreciated.