To get a good rating on your download speed go to www.speedtest.net and post the results here. You very likely don't have a 100Mbit connection, that is mostly likely just the speed you are connected to your modem at. You should be able to lookup what speed you pay for from your ISP's website.
The fastest offering where i'm at is 50Mbit which is $100 a month just for reference, and that's in a fairly developed area.
As boone145 mentioned rebooting the modem is always a great first troubleshooting step.