* Restart your computer if you haven't already.
* Try an external USB keyboard if you have one to see if there is any problem with that.
* Open Device Manager and update the keyboard driver(s),
* or go to dell.com support and put in your Service Tag to get a list of drivers (or use the automated tool on the Dell site to scan your computer and suggest driver updates) and update from there.
* If the keyboard still isn't working at that point, see if you can get into the BIOS diagnostics and test the keyboard there.