To switch it back
login into your account in run level 3, or just wait till its booted and you see the blank screen then hit alt+cntrl+f2 (f3,f4,f5,or f6 any of those. f7 is for your X11 screen)
once your logged into your shell type 'switchdesk kde'.
As for why gnome gives you a blank screen i have no idea, assuming maybe it wasnt installed or not installed correctly when you ran the install disc.