Hello and welcome to Bleepingcomputer.
Lets see what this error means.
Here are the two results this error is related to.
No.1) 8042 Gate-A20 failure: BIOS cannot switch the CPU into protected mode.
No.2) Keyboard controller Gate A20 error
You can check the codes on this page for reference.
Do you have another keyboard handy that you can try to see if this error goes away?
You should also boot your computer into the BIOS setup utility and check around in your menus for GATE A20 OPTION to see if it is disabled. It should be either set to FAST or NORMAL.
Because BIOS menus are set up differently,(specially with Dell computers) I can not tell you exactly where in your BIOS menu you will find Gate A20, but if you look around a bit, you'll find it.
Let me know if trying another keyboard, or at least making sure this one is properly plugged in, resolves this error.