I'd get onto HP UK about it were I you as they might refund the price (or extend/enhance the warranty) of your new machine - and with the cashback you'd be up on the deal
.
Worth a try I'd say - personally I'd take the approach that you probably wouldn't have bought HP again if you'd known about it & its going to take something for them to earn your trust again.
Oh & the customer advisory notice does exist but after HP's recent split it exists on a different server :
http://h20564.www2.hpe.com/hpsc/doc/public/display?docId=emr_na-c03199591&lang=en-us&cc=usA brief quote from it :
In very rare instances, the SATA Power Y-cable (HP Part Number 456853-001) which connects to location P6 on the power supply of a ProLiant ML110 G5 server and is used for powering a third and fourth SATA device, may fail even if it is not plugged into a SATA device. If this occurs, the server may not boot and the cable may become damaged inside the server chassis. In addition, the failure of the cable could, in rare instances, cause the attached peripheral device (SATA CD-ROM/HDD) to fail, fault, or become damaged during normal operation.
Sounds like that's the one, doesn't it?
Edit2 - "Cables that were built after May 2011 are properly functioning cables."
Get an email over to HP and ask for compo is my advice.