You need to figure out if it's the wireless going wrong or the broadband connection itself, e.g. by plugging in something directly to the router and seeing if that's ok. If it's just the wireless then it might be the router failing, or it might be interference from other nearby users. If the problem has just started up it could conceivably be someone new using the same channel as you. As I posted before, if you are using 802.11g, then preferably try and use channels 1, 6 or 11, because these are the only non-overlapping channels, the others all overlap with at least one other channel.
With routers, yes, you usually have an http:// address that you can go to which will get you into the admin system of the router. This requires a password but there's usually just a default one that should be in the instructions (or even possibly on a sticker underneath the router) unless you've changed it.
If, however, a PC plugged directly into the router has the same problems, then it's probably the broadband link itself, which you can speak to your ISP about.