Computer will not connect to the internet

My parents computer periodically will not connect to the internet. They have dsl, and live in a rural community. They usually call the man who runs the business from which they purchase their dsl services. I spoke to him, and he said what the problem is, is that sometimes they reset the isp numbers at their business. He also said that usually they can reset the numbers on my parents computer from his business-but for some reason, he has to reset it manually on their computer. Anyway….once again, their computer will not connect to the internet. What could be causing this? What else could I do, to get them online? Any advice is appreciated.

What OS do they have on thier system?

this is not much help, but i dont get it. a isp provides a ip address- a unique number for each subscriber. having to "reset" the numbers makes no sense (to me) a isp shoudnt be able to "see" anything past the modem they provide you with or a modem you purchased.