I notice we have different models of toaster but both toasters have the bread being inserted from the top of the toaster. Mine had a similar problem a few weeks ago. The problem with my toaster was that it was not getting power from the electrical socket in the wall. The reason the electrical socket was not giving power, was because the GFCI had tripped. The GFCI on the electrical socket had a reset button, so I tried that, but it didn't work at that time. I found out later that the reason was that I had too many things running at the same time off of that one electrical socket (microwave, George Foreman electric grill, and my toaster). My toaster would not stay down unless it had electrical power coming in from the plug.
My solution for you is this. Check to see if the electrical socket that your toaster is plugged into has a GFCI on it or if the circuit breaker for that socket is tripped. (A GFCI electrical socket looks like a regular electrical socket that has 2 buttons on it. The 2 buttons will be labeled "Test" and "Reset") If the GFCI is tripped or you cannot tell if it is tripped, then press the "Reset" button all the way. You should hear a click if the GFCI was tripped. For circuit breakers in your circuit breaker panel, the best way to make sure they aren't tripped is to move the lever all the way off, then move it all the way back on. If when turning it all the way back on the circuit breaker did not fight you and did not click off again, then the breaker should be sending power to the electrical socket.