whats wrong

I planted 4 bag seeds and vegged them under 2 of the 24'' grow lights frow walmart and they were looking really good but was about to out grow there space so i built a 4' x 4' x 70'' high box and ordered a 400 watt hps. anyway i stuck them in the box yesterday and turned light on and came back like 30 min later and all but one was fell over and looked awful, the temp was around 75 in the box at the time and the light was about 1' over the plants and i could hold my hand at the top of the plants no prob.so i was like shit and tured the light off, came back like 2 hours later and they was looking a bit better but sill not good so i turned the light back on and the same happend agin.what to do temp has been around 75 the hole time.

400 watt,should be at least 18inches above the plant,add ventilation if theres none.

possibly move the light a bit farther from the plant. think you might have over/under-watered?

for the first week or so keep the light about 25 inches away and let the plants get used to it, then gradually move it closer until its about 12'' away