Help!! Plant is dying

Help! Plant is dying APPRECIATE YOUR PROFESSIONAL INPUT AND APPOLOGIZE IF I SOUND LIKE A JACK ASS. BUT I HAVE A 4 WEEK OLD FROM SEEDLING PLANT. HAD TWO BOTH HAVING SAME PROBLEM, 1 RST ONE THAT Died started getting week at stem and upper leaves turning yellow then withering down and then plant just dies. It happend so quik less then 2 days from looking great till dying, other one heading same direction just slower don't know what to do using CFL flood 18/6 ights growing in mixed outside soil with m.g only difference in both is the one that's still alive is older by a week and the younger has a hotter CFL lamp then other.
 
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