In 2nd week of flowering went in my room and one of my plant wilted dryied up and turning yellow :`( can i save it
Possibly , but you might have to switch it back to veg .
Why would it do that?
Mot 100 % sure but broke ph meter rwaiting for new one
Not enough water maybe , when in flower plants seems to use water more faster than veg .
I have a 20 gal rez so they have enough water it was also hot in my grow room i think shes done im just woundering why this plant did this and others did not
Heat will kill , you have to get air moving in & out of the grow space , an inline fan is very important to control air flow, heat , and humidity . You can used an inline duct fan 6’ to bring air in , and the inline to suck air out depending on tent or grow space . But if it was due to heat , I’m not sure why when you growing in hydro . I think Mac G is the hydro guy or Latewood , but they can help you more than I can , I’m just half way through my first soil . When I do try hydro , I’m using the advance grand daddy ph perfect system .
I agree with Toshi they will drink more when in flower and heat get that air moving
Will
I think it is advisable for you to fill out a Support Ticket, and we can help you in a much more informed manner. 
Peace