[comtrjl]

A completely new installation of Calibre on 32bit Windows 7:
Registry entries (only 1):
HKLM\Software\calibre containing the installation directory: c:\program files\calibre2 (for 32-bit Win 7)

Also creates 2 directories:
c:\users\<username>\appdata\roaming\calibre
c:\users\<username>\my documents\calibre library

Adds c:\program files\calibre2 to end of path

So you should have this and no other reg entries or directories. The old calibre directory (c:\program files\calibre) shouldn't exist. The path entry probably only matters if you run anything from the command prompt.

Under Win 7 you can still press f8 and run in Safe Mode and calibre can be run in safe mode. See if that makes any difference.
You can also still run 'msconfig' and temporarily turn off anything which starts automatically and see if calibre behaves any differently.
Personally I would look closely at the anti-virus: turn it off temporarily or add calibre directory to the excluded items, or at least the main program.
Also check the event viewer: perhaps the same problem affects other software.
Try right-click on prog and run as administrator.
Check temp directory is set properly and that calibre can write to it.

Edit: reminder from theducks that for 64bit systems, path will be ..\program files (x86)\... Thanks.

bob