"X is not a valid Win32 application" Error on EVERY executable

When I try to execute ANY ( yes, any ) executable ( *.exe/*.msi etc) file, I
receive the error msg "is not a valid Win32 application". I am now at the
point I can not add or update ANY software whatsoever due to this error
coming up for any executable.
Im running Vista Home Basic, I thought I was a power-user until this one,
and my goal is to either A) Find out the problem and a fix for it. -OR- B) If
someone could explain what a valid Win32 app is- I may be able to figure it
out from there. The online services have been NO help. MS help does not say
why this error happens other than corrupted files ( but eg: if I compile a
functional C++ script to an exe, that too is "not valid" ). So ANY help or
IDEAS on a fix for this, or just what it MEANS would help.
Ironically, I work in tech support, and I know my way around windows on an
intermediate / trained level. This is making my laptop a paperweight, any
ideas appreciated! Thank you so much!