Thanks for posting. Apologies that your system is not performing as expected.
Please post your system's Model number so that we can give a more complete answer to your question.
Here is a few things to try:
Perform a systems diagnostics by running Dell SupportAssist, make a note of any error messages encountered and post back. If there are none, then make sure your modem and router have been reset and are connected to the internet. You can check this with another device.
If all that's good, then here is information from the Dell knowledge base you may find helpful:
If the system is under warranty, please contact me privately. Be sure to include your personal information (name, address, telephone, email) and your computer's service tag number in your message. Thanks.
If there is no warranty, then you could contact our Out of Warranty team to get a quote for a paid service call -http://dell.to/1vnT6CQ