You may have already resolved this by now...
Can't be certain what is happening without more information. The best way to figure it out would be to connect the P2140 to a laptop and run PSUmoni. See what states the power supply is entering prior to shutdown.
Here are some instructional video from the Carnetix site that may help and a link to PSUmoni utility in case you don't have it installed.
Let us know what you find.