fldanger

I have a 2011 alienware m17xr3 originally with a gtx 560m.I changed graphic card to gtx 880m. I have a unlocked bios version 12. I already shut off the audio, changed sg, to peg setting and disabled the internal video card. I have tried to install a gtx 880m mod driver but because the device manager doesn't reconized video card it keeps telling me that no hardware installed. What are my options to fix issue.