my internet wasn't working, other computers are fine

So Thursday afternoon after school, i go onto my computer and i had realized my internet wasn't working, all my families computers were working fine, i changed ethernet cables, nothing happened, my mom has a mac and the internet is fine. I went into Network settings in System Preferences and i went into network assistant and i chose "Ethernet Cable" and my internet has worked for a couple of seconds, i went back and did it again, and it went to internal modem, so i kept doing it, and it kept reseting to internal modem, its hard to explain. Im using my five seconds of time to ask for help here, how do you reset your network settings?, is my computer screwed?

Thanks,
Mick.

Have you tried a different network cable?

Yes, and if i choose a new location, i have internet fpr 5 seconds and then it claps out.

Try resetting your PRAM (reboot and hold down Command Option PR at the same time BEFORE the chime).

See here and make sure you hear at least 2 chimes per this - Resetting your Mac's PRAM and NVRAM

Mick - to get help you need to be specific - all my families computers - is not telling us anything. My guess - your computer is not screwed but someone needs to sort the settings on your LAN. Who set up your Mums computer, get them to sort the settings and remove the conflict/s.