quik easy way, disconnect the pwr wire from amp, touch 1 prong from multi meter (set on continuity) to pwr wire, connect the other probe to a good ground, if it beeps you have a break in your pwr wire, a screw through it, or its broke.
Now if nothing happens, connect 1 probe to pwr wire at front and 1 pwr wire at back, this time your looking for a beep, then check resistance, should be very low if not zer0.

is the amp new?
is the amp reputable?
could be power supply failer in the amp
could have pwr and grnd wire reversed accidently causeing failier


fuses dont just blow by them selves so that means thier is a reason, find it and problem solved