What is your volume knob linked to?
check the SYSTEM menu, page 6
make sure that "Power Amp" is ticked (and watch your level!)
What Ingolf said :
-plug a speaker cable from the red output jack to the cab
-press the 'output 'button and go to page 2/6 that make sure that "monitor Out Link " is on ( dark )
Now turn the Master Volume knob clockwise and your done ( I hope 
Ok, I found the "power amp " setting. It's under output, not SYSTEM. It's on. Still nothing
of course it is...
my bad.
Could be something with your connections. Make sure you're using a speaker cable from the power amp to your cabinet.
SoulDesign: I have the same problem... I contacted burkard already.
He said, that I should reset the init globals in the system menu.
Unfortunately, I cannot test it till next week. Maybe you should give it a try.
Can someone confirm if resetting will wipe my rigs though?
A system reset (init globals) won't wipe your rigs.
As always, do a backup before doing anything that's system relevant (this includes updating as well).
OK, i did a global reset, and still nothing. 
OK, i did a global reset, and still nothing.
now it's time to speak to support again.
same here... nothing happened after resetting the globals. I'm going to answer Burkhard...
Sometimes when my Power rack doesn't give a sound ( in Browser ) I turn the Knob back on "tuner "and again back to "Browser " and sound its back again. ( You could try this ?)
Is this some kind of bug? Has the power amp malfunctioned? Is this user error? Keen to find out, given that other users seem to be having similar trouble.
Ok guys, i was having the same issue and i thought my Toaster powerhead had a problem BUT as i was going through the output options on page 1, I realized my monitor output was off! I turned it to stack and it works! Hope that solves your issue 
Just had this problem, and you solved it. Perfect. Thanks! My Monitor Output had somehow been set to off...bizarre. Never even used the menu before so I have no idea how my speaker output had been shut off on my PowerHead...
Ok guys, i was having the same issue and i thought my Toaster powerhead had a problem BUT as i was going through the output options on page 1, I realized my monitor output was off! I turned it to stack and it works! Hope that solves your issue
This is the solution that worked for me, just to be clear. Thanks again.
After thinking about this issue last night after getting it solved, per above, I wanted to add some context,
I've used the Kemper for over a year now...including gigging to multi-states, large and small venues, etc. At band rehearsal last night, I plugged the unit in, and got no output from the powered output designed for external speakers. First time this ever happened. I was perplexed, and did not know what to check since I've not really experimented with the various output/input menus and other stuff - the unit has always just worked for me. I had to borrow an amp for the rehearsal session. It was quite frustrating.
First thing I did when I got home from rehearsal was to do some basic searching on the issue. This thread took me to the solution above regarding the Monitor Output setting being "OFF". It worked, and the Kemper is back up and running...however, I remain perplexed as to how the unit got into that state? Is it possible something else I may have done could have caused that to happen in between rehearsals?
The only change I know I made in that timeframe was to go into the output section on Page 6 to increase the volume for Aux-In so I could play some music through the Kemper for practice and learning songs. In this case, I turned UP the Aux-In Main as I use the main outs for my studio monitors. I went back into this section today, and found that this setting had been turned down to 0 as well - without my doing it. Very curious...
Does anybody have any idea why the output section could be adjusting itself and turning things on and off without user intervention? What might cause the unit to reset elements of the output section?
Anyway, I wanted to document this in case there's a broader issue. I've been treating the Kemper as a "plug and play" unit for the most part, and I'm bewildered at why all of a sudden things are being turned off without my intervention. If someone else has this issue, I'm hoping providing this context might have value...
