Well, I seem to have gone one better than "OMG - OMG I can't login", although not on my operational site just my local one.
I was trying to move the log in box from the front page to the members page in "blocks - login - edit". Clicked update and now can't login as all I get on the front page is "Home". I've tried going to "mysite/user.php" but just get the same, "admin.php" give the usual "you can't access this".
My next move is a complete re-install of Xoops?

*smile* if it's a test machine, reinstalling might be the solution. a good lesson to really understand xoops..