Guys, thank you for your replies.
I tried to disconnect DVI cable and to connect it back again, very slowly, screwing down every side simulataneosly. Didn't show any imprvement in red color.
There are two HDMI inputs on receiver, I tried to change them, didn't help either. It would be very weired if two receiver inputs would be damaged at same time...
Projector I eliminated from this equation, since it shows red, when I swap video input on AV receiver. This tells me, that HDMI out on AV receiver, HDMI cable and HDMI in on projector are fine. This must be DVI->HDMI cable then... Not sure, how it can suddenly break, however. Do you mean the cable itself broke? or is it connector?.Should I visually see somethin if it is connector?
By the way, is it ok to unplug and plug in HDMI and DVI cables while AV receiver and HTPC is on?