TFT Randomly Switching Off?

i have a small problem with a spare tft monitor. sometime it can work for days other only 5 minutes, it seems that it just switches itself off for no reason, i have thougt that it could either be.

1. like when you depress the button on a laptop the sceen jus goes black but under certain light you can stiil see what on the screen,

2. basic loss of power

what can be the problem

can anyone point me in the right direction with either scenario???