Puzzled too cause netgear uses 192.168.1.1 by default and so does the hg612 wouldn't that clash anyway i manually changed netgear's address to 192.168.1.2 is this correct? and put the hg612 back to 192.168.1.1
Yes, any two devices with the same IP address will clash and the end result would be undefined.
However, after downloading a copy of your screen-scrape from the Netgear router (so that I can see it easily), I have noticed something not quite right. With either the HG612 or the VMG1312-B10A in use as just a bridging modem (both keeping to their 192.168.1.1.default IPv4 address) you have, quite correctly, set the Netgear to have a 192.168.1.2 IPv4 address. (It could be anything on the 192.168.1.X subnet, anything other than 0, 1 or 255 for x). Now look at that screen, in the section below where you have ticked the box for the Netgear to be the DHCP server, and it can be seen that you have not changed the starting IPv4 address for the DHCP pool (of addresses for the server to hand out). It is still set to the 192.168.1.1 address. That is wrong. It needs to be 192.168.1.3 (or greater).