Inspiron 1525 Windows Vista with Virgin Wireless Broadband- Can't connect to the internet beyond a local connection.

I share a wireless router and modem etc. with my flatmate and she is having no problems with her connection at all, which leads me to believe that it is the computer (laptop) that is the issue. A friend was sorting some upgrades from me and since then the connection hasn't worked. I have tried a system restore but it hasn't helped with the connection. I ran a diagnositc from the Wireless WLAN [...] Utility and the hardware is unaffected but the disgnosis fails at the Gateway IP ping. I have no idea what that means and I'm stumped as to how to fix it. Can anyone help please? Also just to let you know, I'm not good with IT or computer systems and will need to have most things explained. Thank you.