One of the GFIs in my kitchen is fried and the 3 connected outlets also do not work. The only time I use the outlets are with a toaster and occasionally a handheld electric mixer, and neither of them seem to be defective. Nothing was out of the ordinary, other than a brief thunderstorm early one morning, but I don't recall hearing any extremely close thunder. What would have caused this to happen? Should I be concerned about a bigger issue? I rent my home and I don't want to bother the homeowner if it is something minor. Thank you!

Did you try pressing the reset button? Did you try reseting the breaker?

Bother the owner. It is their job. They make money off you and sometimes they need to spend some of that money to fix problems.
This is one of those times.

Did you try pressing the reset button?

The buttons wouldn't move at all but the receptacle seemed loose, which I had never noticed before. When I took the cover off there was black soot on the left side of a little metal contact.

Did you try pressing the reset button? Did you try reseting the breaker?

And I reset the breaker when I first noticed one of the outlets wasn't working, but before I noticed the GFI was fried.

Is receptacle in metal box and if so is metal box grounded?

No, it is a gray plastic box.

black soot on the left side
That's on the side with the white wire, right?

Make sure wire it tight under the screw.

Yes, the white wires are on the left side.

All the wires are tight, including the grounding wire.

Can I just go buy and install a new GFI outlet? Or should I know what caused this first?

Turn off breaker, remove outlet from box, look for black wire that might have come loose and contacted white or ground.

Was outlet in use or were you plugging or unplugging an appliance when this happened?

All the wires are still tight. I do not know when it happened. I only use the toaster on a regular basis on this circuit, and the last time was 2 days ago.

Can I just go buy and install a new GFI outlet?No. You shouldn't be touching anything electrical in a house that your rent.

CALL THE LANDLORD.

Stan is correct, you have done as much as you should. All indications are that this is the result of a voltage spike. Call the landlord for repairs.

You are both right. Thanks for your help.