Yeah booting the Windows 7 install USB via bios selection.
Used Darik's Boot and Nuke on the drive to give it a full wipe to start a fresh. Tried the Win7 install as usual in AHCI and still hangs before starting to install.
Will now try an OSX install to see if that even starts as I don't know how a HDD that used to install in AHCI mode now has just stopped doing it.