To find your specs, go to "Start->Run and type in dxdiag then hit enter. The info we want is Operating System, Processor, Memory on the system tab of dxdiag, now go to the Display tab and copy down the name of your graphics card" -ScottJC
Also yo might try to unistall the emu from scratch and install it again since you said a few weeks was working good. Since it was working fine, haven't you upgraded anything on your PC lately, software, drivers or even new hardware lately?