I'm going to rage. I want to punch my monitor. "PLEASE INSERT CD PLEASE INSERT CD PLEASE INSERT CD" IT'S IN THE DAMN DRIVE
I know for a fact I got Diablo to work on this computer before but I don't remember how I fixed this issue. Cracks don't work, compatibility makes no difference, disable visual themes, run in 256, etc etc etc. Yes, I tried manually updating to 1.09, also a fail. I have in the past successfully installed and run Diablo and had it update automatically when I connect to bnet and I certainly didn't have to use any stupid frontend loaders or any of the other crap Google is trying to foist on me during my endless searching. Why does it think my CD is not in the drive and why does manually copying diabdat.mpq to the Diablo folder not fix it (it complains about this file when I inevitably click 'cancel'...which by the way I'm starting to wish was labelled F**K YOU DIE IN A FIRE)
EDIT: LOL I fixed it by turning off compatibility mode and disabling my dual monitor setup. The annoying thing is I was pretty sure my secondary monitor had something to do with it last time, but I forgot to turn off compatibility so it wasn't helping me this time around.