built in mouse

You'll need to provide at least the system model and exactly what "not working" means.  The statement is too vague.

If you have an external mouse, try using the Device Manager program in Windows and check if you can Roll back the mouse driver.

Drivers are a piece of software that allow Windows to recognize and utilize your hardware.

If you cannot roll back the driver, you can try installing it from Dell's website.

https://www.dell.com/support/home/en-us?app=drivers