I have a dell dimension E521 and one day my mouse and keyboard stopped working. I thought it was the mouse and keyboard but no they work fine on a different computer. I then thought it was the motherboard and purchased a new one replaced it and still same problem at start up it would say
"Drivers error (0)
keyboard error found"
and i can't do anything.
It could be a USB issue. Go to Dell's support site, select your computer model, and then find the chipset for it. Download/install the chipset and see if that works. Re-installing or upgrading the chipset resets the USB controllers. If it works, it was an issue with the USB controllers.