oh fuck. i'm a dingus.
the primary monitor is actually connected with DVI (at pc) to HDMI (at monitor)... meanwhile the secondary monitor WAS connected via DVI (at monitor) to HDMI, connected to an HDMI to Mini-HDMI converter at the PC. I've just tested the DVI to HDMI and it works just fine... meaning either the Mini-HDMI converter plug is broken...
...or the port on my graphics card is -_-;;
uh. hm. maybe it's neither. because now both are working again... ... granted I did switch the HDMI (in monitor 1) to DVI cable for just a straight DVI to DVI cable... and now it's working. bloody heck I didn't want to deal with pc crap today but here I am I guess aaaaa. at least it's working again now