Why won't my iphone 4 connect to itunes?

The last time i synced my phone was on Feb. 13th. Ever since then my iphone doesn't connect to itunes which causes it to not sync.
When i plug in my iphone to the computer (desktop, windows 8), it connects and charges on the computer but again, doesn't connect to itunes. I'm curious to why this is happening?? my phone and itunes are up to date but wont connect with each other! i've tried using different cords but still won't work!! I've tried uninstalling and reinstalling itunes as well.

My friend has a laptop (windows 8) & an iphone 4 as well andso when she syncs onto her laptop, it works for her.

Why isn't mine working anymore? Does anybody know how to solve this? 😟