This is a very simple unit: a power source of an linear design, a preamplifier with tone and distort control and an 10 watt integrated amplifier.
If the unit is completely dead then the fault is in the power section: cable, switch or source. To find out which you must check them all with a simple multimeter: cable and switch with an ohmmeter (the resistance should be 0 if good) and the source with a voltmeter - (check the presence of the 2 voltages (25 and 15 volt) at its outputs.
Here you can find the schematic of a very similar one
http://www.schematicx.com/view-schematic/fender-frontman-15g-15r-guitar-amplifier-schematic/
The only difference is the final amplifier chip.