Ubuntu :: Can't Access Admin Privileged Applications

Whenever I try to do anything that requires administrative permissions, including Synaptic, the Update Manager, or installing something on the Software Center, the "Starting Administrative Application" task comes up on the window list, but then the window does not come up and whatever action was supposed to be taken does not happen; no error messages, nothing. Also, whenever I use su or sudo in the command prompt, nothing shows up when I type my password; then when I hit Enter, it gives me an authentication error.

EDIT: It seems that the "Add/Remove Applications" program as well as the Software center do not have this problem. Synaptic and the Updates Manager, however, still do not work.