Few more things to try:
Try hitting + to make the manipulator bigger, although that just lengthens it I think
Try holding the ` key to enter tweak mode (or something like that) where clicking and dragging will move the object regardless of the manipulator being selected.
Finally, if it's a question of getting the right axis, you can click on the correct axis (take a few attempts if necessary), then once the axis is highlighted in yellow, you can MMB drag anywhere on the screen to move along that axis.