Try adding a check so it doesn't repeat itself
local DXShowing = false
function Imagen_al_morir()
if DXShowing == false then
DXShowing = true
addEventHandler("onClientRender", root, MuerteSistema)
end
tempo = 30
setElementData(localPlayer,'tiempo_de_respawn',tempo)
setTimer (function()
tempo = tempo-1
setElementData(localPlayer,'tiempo_de_respawn',tempo)
end,1000,30)
setTimer (function()
DXShowing = false
removeEventHandler("onClientRender", root, MuerteSistema)
end,1000*30,1)
end