RainbowMan wrote:
I reset the bios and reflush Dell the PSU and MB( because some voltage still left over even though I completely turned off the system as some online user recommend) and tried again it was working again. I thought I fixed finally but the next morning I turned on again this time it is completely dead. But the PSU still ok and the MB is ok too. I am using 24-pin other PSU and no problem.
Only adjustment is I converted 4-pin PATA pinout to 15-pin SATA (since this PSU only has 2 SATA cable) and the strange thing is Windows reported SATA drive as PATA drive I guess since the 3.3V orange wire is unconnected.

On SATA, the 3.3V rail hardly matters.

Both SATA and IDE drives of the 3.5" variety, use
5V and 12V on the SATA. At 2.5", 5V alone is usually
sufficient for the task (even on SSDs).

3.3V is used on some SSDs with microSATA connectors,
which is a case where you'd want the 3.3V to be present.
I have not seen a reference to such things for some
time, and suspect they disappeared from the market.

And there is one other case where the 3.3V is important.
PWDIS.

https://web.archive.org/web/20181223...isable-pin.pdf

"There is a simple fix if you find yourself in a situation
where an Ultrastar SATA HDD is not spinning up.

By using a simple “Molex to SATA” power (no 3.3V power...)
connector (Figure 1) to supply power to the HDD, you can usually
eliminate the problem. Changing the power connector effectively
removes power from P3 (Pin 3) and allows the drive to spin up
normally."

A pinout listing PWDIS is shown here. I think Pin 11
can drive a LED, as an activity indicator, but I've not
heard of anyone hacking that and proving that all drives
have that capability.

https://pinoutguide.com/Power/sata-power_pinout.shtml

Paul