hi im new to this so here it goes

i have 78 xs400 and it won't startwhen i turn the key i hear a click but ...nothing happens any help would be great!!

thanks

check battery & fuses ,

Starter relay? Find out where it's located and put your hand on it when you press start. If it gives a good click and vibrate you've probably seized up. If it is free then you could be looking at a very tired starter motor.

I would think battery first, but quicker to re-install the glass fuses first as they do corrode easily!