MY Primary DNS Server not responding.

I connect to the Internet with a SMC usb thing which is no problem during the week days from 7:30 am till right around 5 or 6 pm but never on the week ends. After the pm time my computer goes from local and Internet to just local which means I do not connect to the Internet. When I click to see what the problem is it says that my Primary DNS Server is not responding., or it can not connect to my Primary DNS Server. The other day I got one that said my connection was timed out. This is driving me nuts. I connect to Linksys unsecured network. Can someone please tell me how tio fix this problem as I am in a online college program and not being able to connect to the Internet over the week ends is seriously damaging my grades.