I press w key to use move tool,when I drag the manipulator handle x(y or z)to move object(face or vertex),it moves,but after that the manipulator disappeared(look at the left tool box,it has been select tool，the arrow icon),if i want to go on moving,i have to press w key again and again.scale and rotate tool have the same problem,too.I use NURBs modeling objects these days,two days ago,everything is all right,i don’t know how it occurs.and because of that,when i use the round tool across boundary edges of two faces’ in the workspace,it failed,it just selected one NURBs face.
i have try some ways to solve it,for example:reset tool,restore the setting, delete the maya document in My documents,reinstall the maya programme,but the problem is also,it is useless.i don’t know why,can anyone help me,thanks a lot.............

This problem arrives after a gap of some days....and then everything will run fine.....

idk....