Empty the sink and carefully examine the pipes for the leaky joint.
Take it all apart - clean the trap in a bucket (don't use the sink!) and put it all back together again. One of the pipes has probably been knocked and is causing the leak.
The fittings are easy to take apart by hand. A damp cloth helps with the undoing and doiing up.
Put an old towel down to catch any spilt water.
If any pieces are too bad to reuse new fittings are quite cheap at a DIY/Hardware store.
Peccavi
January 2009