Saved FAQ from Freescale.com for information only:
Topic: Evaluation Boards, Power Supply
Question. For i.MX51 EVK, when booting from SD, can't get the OS start - the power led lights for a moment then shuts down.
Answer. Please try to set ON SW10 of S1 boot switch. [The board will turn on immediately when the power plug to the 5V power jack (J1)].
i.MX Applications Processors > i.MX51 Processors > i.MX512, i.MX513, i.MX514, i.MX515, i.MX516