Pioneer m-770 will not turn on

Question

i have a pioneer m-770 amplifier and as i was playing music it turned off now wont turn on, i opened it and check to see what was the problem and one of the fuses was blown. i replaced it wth 250v fuse from radio schack but when i turned it on the fuse blew and then then i tried swicthing to a 125 v that belonged to the amp but the transistor blew also, i know for sure i need to replace that transistor but what about the fuse and why wont it turn on?