Reinstalling etc won't solve anything, just get you back to where you are.
If your ZCart installation is operational, leave it be. I'm assuming you have edited the admin and store configure.php files and changed ENABLE_SSL_ADMIN, ENABLE_SSL_CATALOG and ENABLE_SSL to true?
Another useful step is to head to the /www/webXX/ssl folder in a terminal window/command line, and type in
openssl x509 -noout -text -in nameofcert.crt
which will list out the certificate contents. (the actual cert name should obviously be inserted).
Similarly for the CSR
openssl req -noout -text -in nameofcertreq.csr
And the following 3 can be used to check that the key, the CSR and the cert match
openssl rsa -noout -modulus -in nameofprivkey.pem |openssl md5
openssl req -noout -modulus -in nameofcertreq.csr |openssl md5
openssl x509 -noout -modulus -in nameofcert.pem |openssl md5
Also, bear in mind that where certificates are concerned, www.mydomain.com
is NOT the same as mydomain.com.