Wireless internet

Hi I have a problem with my internet. When i connect my laptop and pc to my Cable modem it works fine, however if i connect the cable modem to my netgear wireless router, It works ok but it keeps crashing on websites and saying server not found. The router belongs to my brother so yesterday i told him to reset it and he did. But the same thing happened again. We had a free upgrade last month from 2mb speed to 10mb speed but the speed is slow now. I phoned virgin media today and asked them why is the speed slow and they said they are doing maintenance in my area and they said i shouldnt be getting the message server not found. She told me that i shouldnt be using the wireless and if you buy a router of your own then it doesnt support virgin media modem. I told her ive been using my router for 3 years now and no problems. She told me that at this moment in time the settings on your router dont support the cable modem. It doesnt make sense to me because the internet should work fine with the router. Why does it crash very frequently at any web page and say "server not found". I dont understand because we have tried just about everything but it seems this problem is happening only with the router. If i buy a new router im not sure if it would still work. Does anyone know of this problem? or can tell me how to fix this?