None of them seemed to make a difference, so I was up late surfing around and came across these DVD tools

They look like they will probably most fix DVD problems, but seem a little complex, so will have to read up on them in some detail before I tackle anything - still I have all the discs backed up to hard drive, so eventually I should be able to fix.

PgcEdit - ' The Swiss Army Knife of DVD Editing' - download standalone .exe , manual and plugins - PgcEdit is a DVD IFO and Menu editor designed to allow the modification of the navigation commands and parameters of an already authored DVD structure.
PgcEdit is also an excellent tool to learn how a DVD works, with his powerful Trace function.
Since v0.6.0, PgcEdit is also the first program able to burn a Double Layer DVD-Video on DL DVD+R or DL DVD-R, with an interactive interface (including a preview), to select the position of the layer break.
http://download.videohelp.com/r0lZ/pgcedit/

ReJig - ReJig is a Windows GUI based MPEG-2 transcoding utility using compressed domain transcoding(recompress MPEG2 to MPEG2). It also supports DVD9 to one DVDR transcoding and basic DVD Authoring and VOB demultiplexing.
ReJig http://www.videohelp.com/tools/ReJig

I've emailed them to you in a zip file attachment via 'yousendit' (about 4 MB)

Johnno