KRELL 400xi - front panel problem...

I just bought yesterday a new KAV400xi. It’s great and sounds awesome. However I have no idea what happened but after a long listening today I observed that I can not choose a source from the front panel – the button S2 and B1 just stopped responding. But I still can choose S2 or B1 using remote controller – no problems with that and sound still goes on great. I tried to unplug amplifier fully and check if that would help but still can’t access S2 and B1 from the front panel. It seems quite weird to me. Have I blocked anything manually? What should I do? It’s not really killing me as I still have the remote to operate but would like to know if I should avoid anything? And there was no electric shock either from my side....
Later on I noticed that if I press front panel buttn B1 for let's say 5 sec. then it goes OK, I also pressed S2 for along time and 2-3 times it went OK after 10-15 sec. of pressing the button.... With remote it is instant - no delays...

In a Krell manualI foundinfo that I shouldnot useany other power chord then the one supplied by Krell. I use XLO power cable - would that diminish musicality of this great amp? ;-)

HELP!

adam