Q: Can't log in or buy music

I have itunes on my laptop and work computer. My laptop works perfectly , itunes runs smoothly, i can get into the store and buy music and even itunes match seems to run fine on there. But when i come to my office pc running windows 7, I cant log in to the store or purchase any music... Error message: 'We could not complete your itunes store request an unknown error occured -50' Pops up in two windows. But i can sign in everywhere else.. Iphone, Ipad, Laptop etc...

What's the probelm!!??? I'm tearing my hair out... This causes issues with itunes match crashing itunes every 2 seconds after opening!

Thanks

Lewis