Computer can't detect iphone 4, only detected as camera

My friend lent me his iphone 4 until i can change my phone, so i went home and connected it to my computer but it only detected it as a still camera.

I tried reinstalling itunes and all other advice suggested by people but it still can't be detected. But when I connected it to my brother's computer itdetected it right away. Anyone knows a solution to this? i owned an iphone 3gs before but never encountered this problem. Any help would be great. Thanks