White screen is indication of your web server or PHP failure.
You need to check 2 log files to identify the error
1. Locate your web server error log and check the end of the file for the error.
Post it here.
Post of the time, it will be missing package on your server or incorrect permission of some file
2. Locate your AbanteCart error log in ../system/logs/error.txt
See what is there at the end of the file.
If there is nothing in those logs, check permissions of main index.php file. It must be 755 or 644 (777 will not work)