|If under warranty call dell and tell them to fix it. I doubt they will. Might spend 4 weeks on tech support trying to figure out what they are saying.|
Did you try another keyboard in the system?
If so and it works then there is little you can do but replace the keyboard.
If a known good keyboard doesn't work and ps/2 you might have to use usb.
If usb then check bios settings, look for legacy or keyboard support or such.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10