Why is my laptop not picking up my Wi-Fi but my iphone is?

I have an 'Acer Aspire One Happy 2' laptop that runs on windows 7. I have just gone to my grans and her Wi-Fi works fine on my Iphone 4 but my laptop is not even picking up the signal. My laptop works fine at the Mcdonalds round the corner from me so why isn't it working here. I even typed it in manually and it didn't work, its not picking up any signal at all

The router in your gran's may be set to wireless "n" mode. If the acer has a wireless "g" card it won't be able to see the router. If so you would either need to set the router to mixed mode or buy a USB Wi-Fi "n" dongle for the Acer
HTH
David