Limited Web Connectivity On Laptop After Installing New Modem?

OS Version: Microsoft Windows 7 Home Premium , 64 bit
Processor: Intel(R) Core(TM) i5 CPU M 520 @ 2.40GHz, Intel64 Family 6 Model 37 Stepping 2
Processor Count: 4
RAM: 3764 Mb
Graphics Card: Intel(R) HD Graphics, 1754 Mb
Hard Drives: C: Total - 461899 MB, Free - 248738 MB; E: Total - 476821 MB, Free - 6 MB;
Motherboard: Dell Inc., 029DYC, , .5CZ41M1.CN1296104U1550.
Antivirus: Charter Security Suite 9.01, Updated and Enabled

I just upgraded to a faster internet speed with my cable company, and so they came and installed a new combination modem/ wireless router yesterday. Since then my computer has said that it is connected to the internet but when I try to load pages sometimes they work and sometimes they don't. Mostly they don't work, and when they do they are very slow and don't always load pictures, video, etc. The other computers and devices in my network have no problem with the internet connection. My computer connected perfectly before the new modem was installed, and it works when it is plugged in directly ( it was plugged in the entire time the cable guy was setting up the network). I tried running the diagnostic tool and sometimes it says that the dns server isn't responding and other times it says it can't find the problem or that it can't find any problem.