Failed internet access using RRAS

I have a lan of about 25-30 computers running win2000 server/professional os.Internet access is got thru a vsat connection to the gateway server.i have used rras to configure internal and external interfaces.Everything worked well but after a while i find that the clients cant browse properly anymore.The gateway server mwl, browses well,the clients can chat using their yahoo messenger.I can ping public internet ip’s but sometimes pinging www.yahoo.com fails, though not always.But the issue is that the clients cant browse.I’ve checked and rechecked all the settings incase they were changed but came up wt nothing.I need help in sorting this out asap pls.