On Apr 9, 6:55 pm, "RBM" rbm2(remove wrote:

snip

Sometimes the tongue
at the bottom of the socket becomes depressed, and the lamp doesn't reach it
to make contact. This would require carefully prying it back up.

snip

9 times out of 10 this will fix it. Failing that, you may want to
replace the sockets with some sturdier ones from an electrical
distributor. Some of the box stores are stocking these also, so check
it out, Good luck.

Joe