Cannot connect to Interent

A friend has given me his laptop to look at. The problem is he bought a mobile internet dongle (usb connected) which worked fine for a while but now it has just stopped working. I brought into my office and tried it on the broadband
(rj45 connection) in the office and that did not work either. I have ran scans with AVG 8.5 and some other freeware but it came up clean. I have done a system restore to a point before it stopped working. OS is Vista home.

Any ideas :confused