My PC is set to "sleep" if inactive for so long----when it does so the red light on the modem comes on.( Should the modem switch off when the PC goes to sleep??) When I bring the Pc out of sleep (by pressing any key) the red light seems to stay on and I get the message on screen----"You are not connected to a server" or "page cannot be displayed". I then have to keep switching off the modem for 10 seconds and back on again. All is fine after that.----Is my modem in need of replacing??
Personally for the convenience I'd probably suggest buying a ADSL router. I've never had this problem before so I'm struggling a bit to assist in any other way other than suggesting to replace it. Either than or don't put your machine into sleep, just turn it off and turn it back on when you need it.
It could be settings in your modem. You should be able to login to it and check them. If you bought the modem yourself the instructions that came with it will give the account name and password (often admin/admin). If it was provided by your ISP you will be able to get details from them.