MY AMP'S CHANNELS ARE SCREWED!!

[HwnCrisp21]

well, not exactly sure how it happened, but my amp is completly dead...
I have a Marshall AVT150hx and ran it through a 1960a cab. not sure why but one day it just made a very loud feedback but not due to the guitar... i turned it off and when i turned it back on, the volume level was drastically lower. didnt think much of it until it got worse... now the amp gets power but none of the channels light up and work. i just hear the normal low buzz of the fan...
wat is the problem with it??? how can i fix this easily??? REALLLy need some help with this as soon as possible!!!

[R.G.]

What you can do depends on your skills.

What amp repair skills do you have?