The reasons for your lack of connection to the Internet could be several, but not only limited to:
1. Problem with the NIC card /network adapter/ of your PC
2. Problem with the modem/router that you connect your PC to
3. Problem with within the network provider
4. Failure in the Ehternet cable that you connect your PC with
Please provide more information on how do you connect your PC to the net usually. Has anything happened to it recently?