@dazjilly first, clean that whole board properly. You pointed out some of the corrosion but we can not rule out that there is more. Check for any damaged components and some of those may need a resolder with plenty of flux. After that you need to check the power rails and see if your motherboard does get power. Be prepared to possibly "fire it up" so you need to reinstall your heatsinks/fan etc.
You have a very busy board, so in order for us to help you sort things out, we need to zoom in closely. Post some very focused and large images of your board. Otherwise we really can't make out the details. I have not found the schematics for this board but have the component layout. That makes it even tougher to diagnose ;-) but let's see what we can figure out.