When I connect my droid 4 to my computer it won't show up currently using cm9
Same issue here. I think it's something with CM9. Try AOSP ROM:
[ICS AOSP ROM] "AOKP" (Android Open KANG Project) for Droid 4 [BETA 3/16/2012] - xda-developers
For me CM9 is much better with Data but AOSP works with USB. Another workaround is to go into recovery and mount USB with an SD card inside. It doesn't work without it for some reason.