@
rckmnr - if neither the 64 or 32 bit versions will start, try the portable version.
If that doesn't work, then something on your computer 'doesn't like' calibre - period. Most probably a 3rd party program that runs at startup, possibly a shell extension, or even a service. Startup programs, shell extensions and services can be disabled selectively - and not all such things are disabled by Windows Safe Mode.
If it does work then you'll have something to work with, portable is the 32bit edition in an 'isolation' wrapper.
Have you tried running a
System File Check
I don't think your problem is related to mine, but Kovid has made a 'just in case' change that will be in the next version, so give it a try when it's released.
BR