Laptop Won't Connect To Mobile Broadband Or Wireless Networks?

I'm living in Australia for a few months and my accommodation does not have a phone line, so I've been using mobile broadband dongles instead. This worked fine until recently, when I abruptly became unable to access the internet. The laptop recognises the dongle and seems to connect, but the download/upload speeds are at a constant zero bytes per second (I have tried to ping Google while 'connected' but received no response). I have tried two dongles from Dodo and one from Telstra, with the same results. Initially, I assumed that this was simply due to signal strength, but each of the three dongles I have tested work fine on another laptop in the same location (I'm using one of them to post this). I have also tried using the dongles with my laptop in other locations, including the city centre, but with no success.

Also, I seem to be unable to connect to any wireless networks (e.g. McDonalds wifi) - the laptop detects the network ok, and seems to be connected, but I am unable to access any web pages etc. In the Network and Sharing Centre, the laptop is connected with the wifi network, but the wifi network does not seem to be connected to the internet. I'm unsure if this is related to the above problem, however.Like I say, everything seems to have been working fine up until about a week agoIf