when i turn it 0n ,it will turn its self off.

MARK, August 2015

It it turn off quickly, I agree for a PSU problem.

If it appens after some time, like several minutes, hours, or under heavy load: Several CPU intensive application running, I'd suspect an overheating isue.
In this case, you need to open the case and clean out the dust accumulated in the CPU's heat sink.

Electro, August 2015

Probably a Power Supply issue - the signal - Power Not OK -causes the machine to turn itself off - a new PSU can be had quite cheaply - just match the Wattage. Second hand even cheaper - 10 minutes to exchange.

Good Luck..., August 2015