Ethernet problems on 2006 Macbook

I have a 2006, 13-inch white Macbook currently running osx 10.4.11. i've been having problems with my internet connection as of late, where sometimes it just doesn't work at all, and sometimes it works fine. it will go off for about 12-16 hours (usually at night), and then start up again at some point in the morning. i'm connecting via an ethernet cable to a modem with a PPoE connection.

Now, I called the service provider and they sent over a couple guys with very little knowledge of apple computers, and told me the problem was with my computer itself. they had typed in a few ip addresses of sites (google, facebook) and got to those pages, but it was not working otherwise. So they said I had to get the computer serviced. The problem is, I live in India. There is no 'genius bar' to take this thing to, and I'm highly suspect of some of the support people at the local "apple" store.

It doesn't really make sense to me that this problem would occur as it is, with this semi-regular disconnection if it was a problem with my computer. It seems to me it's the SP's problem. Does anyone know how I can properly figure this out? Could it be a problem with my ethernet port?