problem opening PDFs

[MARKBLACK]

Hi
Today I downloaded 7.5 PDF reader I already had 7 on so thought I'd upgrade. Now I can't open my PDFs I get a message saying 'PDF is not a valid win32 application' so I uninstalled 7.5 but its the same. Can anybody help me put this right?

MB

[Sylvander]

If you are running WinXP you could "jump back" to a restore point made just before this problem was introduced.
or...
Restore a backup of the C: partition made [immediately or shortly] before the problem was introduced.
[I do this as a matter of routine, and such software problems are simply and quickly undone.]