mpg codec problems

download a program called Gspot - load it and load the vid file and it will tell you exactly what codec you need and where to get it - also will tell you if you have conflicting codecs

Gspot will work only with the AVI and OGM, OGG file container, and does not show information about MPEG-1,2 files. Try firstly to open with VirtualDubMod (freeware), and in the menu "File->File information" will see the information about your MPEG file. File could be corrupted, so VirtualDubMod show some MPEG error. If there are no errors in VirtualDubMod, you can see MPEG file information. If the header shows MPEG-2 information, your system could not include MPEG-2 direct show filter, or this filter could be corrupted. Try to use DVD playback software, such as WinDVD or PowerDVD (all shareware) to playback MPEG-2 files. Some free media players works fine with the MPEG-2 files - it is easy to find them. Also try to find the software for the corrupted MPEG files to fix them.
Post your results here.
Good luck.

For MPEG fixing try to de-multiplex and then multiplex again using TMPEG Encoder
http://www.tmpgenc.com/
and for the MPEG-1 fixing only
http://www.vcdgear.com/download.html
Post results.

Are you sure it's an mpeg-1 stream? Just about any modern OS can handle that with no sweat, but mpeg-2 will need a codec (eg DVD player software will install one) and stuffed if I know how to play mp4

I would suggest the K-Lite Mega Codec pack. It allows me to play anything and it comes with GSpot mentioned above. Do a search for it on the web and I'm sure you can find it for free.