Dell optiplex 3050 and many others, installing drm-61-kmod from ports results in blank screen with some garbage at the top. installing drm-61-kmod from ports works well. using kld_list="i915kms" in rc.conf uninstalling drm-61-kmod in package and building/installing drm-61-kmod from ports solves the corrupted video.
*** This bug has been marked as a duplicate of bug 284115 ***