Why does my dell tower keep switching off after booting up



when i start up my tower it boots up but after about 30 secs it turns itself off what is causing this . the previous owner said it was definetly working am i doing anything wrong when i switch on or is there a fault with the tower. thanks
Welcome to Tom's Hardware Forums,
There are a few possibilities here, 1) something became loose during transit - check all wiring connections within computer to ensure none are loose. Also, check the heatsink/fan on the CPU, ensure it hasn't become loose,
2) the PSU died during transit - unlikely but the PSU would need to be replaced or
3) the seller was exaggerating the condition - PSU would probably need to be replaced.