I've had this computer for a while now, and recently when I started the computer up the mouse and keyboard wouldn't work so I booted the computer up with “Disable Driver Signature Enforcement” and went to the Dell website to see if it was a driver problem. The was one driver I didn't install or update called Chipset| Intel AMT HECI Driver. I tried installing it and it gets to
"Installing Service: LMS
creating process: C/Dell/Drivers/DWW4Y/DAL/vcredist/_x86.exe"
Then after it says "the setup program failed to start one or more application processes. setup will exit Chipset| Intel AMT HECI Driver"
The AMT HECI driver wouldn't explain your keyboard and mouse not working, but if you want to get that driver installed, try updating the Intel Management Engine to the latest version first.