If you can use a multimeter, don't bother plugging the amp in. It sounds like there is a problem. To check earth continuity, switch the meter to continuity and touch one probe to the earth pin, other to chassis - or your guitar strings. No buzz or quiet buzz means a bad earth. You could also use the resistance part of the meter if you know what you're doing.
But it would be best to take it to a repairer before using it again.
It would also be worth checking the socket used, partially by plugging into another socket, preferably in a different room or level from the one normally used.