I will need more information, as there are many circuits inside the TV that will cause this.
How long have you had it for and when did the problem occur?
Additionally, when it shuts down are there any blinking lights on the front of the TV?
I believe we're at an impasse without knowing the board specifically that failed. I can tell you that boards for a set of this age will be near impossible to find, and often times it is more cost-effective to purchase a new flat screen in lieu of trying to repair an older set.
I can tell you that the Flyback transformer, Convergence IC's and CRT (Tube) are what commonly fail on this set. Chances are you only have a problem with one of these circuits and not all of them. Parts for your set again are scarce, but you can use the link below to locate what parts are available for your repairperson to procure them from: