"The network did not assign a network address to the computer"

Help!

My Windows XP laptop was connected to the internet via erthernet cable to a Linksky modem (I've been using my grandparent's internet). Up until a week ago, that's worked fine. But suddenly it's stopped working, and whenever I try to connect I get this:

"Limited or no connectivity

You might not be able to access the internet or some network resources. This problem occured because the network did not assign a network address to he computer."

Could anyone please help me?

ETA: I am completely illiterate when it comes to computers, so details might be necessary. Thanks!