I have an old laptop that won't charge my iphone?

I got an old acers laptop back in 2008 and I haven't gotten a new one since. I have an iphone and a usb cord but the laptop refuses to charge my iphone because it says that it's an unknown object. How can I fix this?

You don't need the computer to recognize the device to charge it. The problem is your laptop doesn't pump out enough current through the port to charge an iPhone, and that is simply an outdated design. USB was never really meant as a charging port and this capability was added much later.