|There should be flashing light on the modem to indicate connection problems that are not PC related. Otherwise try new modem cables.|
Only way to check if it's a faulty modem is by replacing it with a different one.
Same with network card, try a different one.
Always keep spare modem and network card in your drawer for such occasions. I have two spare router/modems, a spare network card and spare networking cables at all times in my spares cupboard. It's the only way to diagnose connection problems, process of elimination.
message edited by phil22