2008 Unibody no-entry sign after boot options

Hi all,

I have a 2008 A1278 which gives me a no-entry sign at boot. After inserting a USB OS installer disk and booting with Option, I can see the SSD and the USB but on selecting either of them takes me back to the no-entry. I also tried the EFI partition which actually takes me to an Apple logo and starts to boot.. THEN back to no-entry.

I replaced the HDD cable about 3 months ago and my thought is that since I can see the drive it wouldn't necessarily mean another dodgy cable?

I have tried disconnecting the SSD and booting from flash, same thing. Also reset NVRAM, SMC, etc.

Hope I'm not the only one with this issue.