My dell 1721 turns off 45 seconds after powering on, help?
Turns off or restarts?
If it turns off then it sounds like a overheat issue or a hardware failure, Could be power related.
For over heating make sure you can feel air coming out of the vents on the laptop when it is on, keep it on a hard flat surface.
can you hear the fan going? they are only little and depending on the age they tend to wear out.
if it restarts then it could be a BSOD (driver conflict or memory address issue)