What could this be Tube Failure

I have a problem with one of my monoblocks that I need some help with. . Upon powering up last night,loud popping static noise started coming out of the right speakers. The (4) kt77 tubes in the corresponding left monoblock started flashing. The weird thing was that the tubes never got to the normal orange color but rather were flashing light blue. I immediately powered down before any speaker damage occured. But I am hesitant to power up again until I know what is going on. Any ideas as to what this could be besides tubes going