Thanks for posting. Apologies that your system is not performing as expected.
Looks like you've tried a lot of things to get this resolved. Have you done a system diagnostics yet? Please run diagnostics by either pressing F12 at startup or by running Dell SupportAssist. Make a note of any error messages and post back.
You may wish to back up your data, because you may have to reinstall the operating system.
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