router not assiging an ip address - how to fix?

Hey,

Using the sticky I've deciphered that my eircom router is not assigning an ip address to my laptop. it was working correctly for a number of months and then suddenly just stopped working, but i didn't install or uninstall any programmes or drivers. just wondering what my next step should be. how do I manually assign a new ip address to the router/computer? not entirely sure what the next step is. ive tried googling for a solution but im not entirely sure what i should be looking for. any suggestions? thanks in advance! even a link to google would be much appreciated, just im not 100% on what the next step is but i would be a little computer literate!