Have you restarted your computer lately? It sounds like ethminer is not detecting your card, have you installed the microsoft c++ redistributables? Leave off the local work and global work to see if that's the problem, probably not. When you didn't have the -G you were most likely mining with your cpu, that's why your MH/s was so low.
I was told on reddit to follow this guide I am on stage 8 of Building from source
