computer won't fire up more than one second with HDD connected

I have a computer with an SSD for the OS and core programs. The rest is stored on a HDD. Recently my wife thought that she smelled burning the other day but there's no evidence of it so could've been something else.

However the computer no longer powered up until I disconnect the HDD. SSD). I thought that it had broken so bought another. Yet when either hard disk is plugged into the motherboard the computer tries to start (1 second) then turns off. As soon as I unplug the HDD's the computer boots again.

Either both drives are dead, or the cables to the drives are flaky or there is a problem with the SATA controller on the motherboard.

• I tried several different SATA cable with the HDDs. No improvement.
• If I put a DVD drive on the power cable which usually connects to the HDD the system works
• If I connect both power and SATA data cable the system fails to boot.

Ancient history: There was an incident about a year ago where there WAS a burning smell and it turned out to be a power cable to the SSD becoming loose, and arcing, but I managed to resurrect that by using a different SATA power plug on the PSU lead (the original lead that was used was an adaptor from a molex or another cable on the psu, and not one of the dedicated SATA leads).

More recently, I noticed that one of the SATA power plugs (on the daisy chained power lead from the PSU) had half its plastic connector part snapped off, so it's possible that it was on the HDD and it fell off, maybe causing a surge?

thanks for your help Hennes, it turns out that every cable to every sata port did the same thing.

In the end, I don't know where I found the answer, but it turned out to be the power switch.

I looked up the M/B manual online, identified which was the reset and which was the power, and swopped them over.

Hey presto, a working machine!

One thing's for certain, if it hadn't been for this website, I wouldn't have been able to fix it.