Hi Bhavik:
If you feel that somebody has hacked your system and using internet, then you can make sure the following things, so that they cannot enter again your system to use your details/to use your internet facility.
1) Make sure antivirus software is up-to-date
2) Make sure you are installing all the Windows Updates regularly.
3) Make sure Windows Firewall is ON.
4) If you are using internet using Wi-Fi facility, then make sure its password protected. Else, with the help of wi-fi signals, people around your home can access the internet because wi-fi signals can be reachable upto around 10-15 houses from your home. So be password-protected for your net, so that no one else can access your net. As you observed that some pages are not visited by you, it might be because some one else is using your net facility, so you might be seeing their visited webpages.
MAKE SURE ABOVE ALL TO BE PROTECTED.