Thanks for the link. It matched so i do have the correct set.
So i decided to go back to the start and used the original retropie image on a diferent card. This time, I left the roms on the sd card rather than move them to the usb. Low and behold they worked fine!!! Couldnt believe it. It turns out that even though i had linked to my usb in es_systems config, i hadnt changed the path in the mane config. Still learning!!
It also turns out i had left a couple of roms on the original sd card and is the reason why some were working.
Ah well, hopefully this may help any noob like me who move mame roms to a usb will see that they also have to change the path in the mame config.