many problems with quicktime

[littlegohan]

at first quicktime 6.1 was working fine

then i brought total training program,and that program uses quicktime to my video
some of the videos dont work.
some work but quicktime will crash when playing them (says quickesstential.qtx has a problem)

so i unstalled quicktime 6.1 and installed quicktime 5.2 on the cd
that doesnt solve the problem either
so i iuinstalled 5.2

now i reinstalled 6.1, and i cant even play files that were once working......
it will say quicktimeesstential.qtx caused a problem..