In device manager, there is a yellow question mark next to 'ethernet controller', does this have anything to do with it?
It certainly does have something to do with it....in fact, it has everything to do with it!
It basiscally means that the network controller card is there, however there are no drivers for it, therefore rendering it un-useable! What you need to do is obtain a driver.
The easiest place is the internet, however you could have some issues obtaining it from there. What I would suggest is using a friends computer and downloading the driver files to a USB pendrive or CD, then installing them from there.
Once you have the driver, you can plug in your ethernet cable and you will be online.
If you have any other questions, please ask.