Hi all!

Quick introduction, I'm a life long casual gamer/retro collector, i'm on a couple of other retro console forums but understand this is one of the largest.
I got my Dreamcast xmas '99 and love it as much now as I did back then. I packed it away in about 2003 and always intended getting back on it but never got around to it but the announcement of Shenmue 3 was the kick up the rear I needed. Once dug out I totally forgot how mad I was on this console! Forgot how much mint condition stuff I have for it!
Now onto the problem I'm having, so I set it up a few weeks ago to the main downstairs TV to find the picture over to the right and had to mess about centralising it manually (this was via the RGB scart)... So I thought the lead had probably developed a fault, no problem I was getting a VGA box anyway so that turned up last week and as I couldn't get to the VGA socket on the TV plugged it into my computer monitor, so it boots up and exactly the same over to the right different screen, different lead, is this a thing with Dreamcasts? Is there a fix? Many thanks in advance for any help!!