Main breaker would not stay on . Electric company came out and said box was fried,does this mean I have to change the 100 amp breaker box?it's at my cabin.my son was there I was'nt. What to do. Bob

Sounds like the panel will need to be replaced.
Sometimes you can get lucky and just change the guts, but if it's older that's highly doubtful.

Call some local guys and get an estimate, unless you are quite handy with electrical work. This is NO job for someone with no experience in this type of work, and you MUST contact the power company to have the meter pulled so the power will be off while changing the panel.