Most of times we get blank page due to memory issue or due to new plugin/theme installation. We need to go through error_log file for this and where we will be able to get the exact cause.
For memory issue, you should just create php.ini file under the document root ie public_html and put below line :
memory_limit = 40M (depend on the the requested value)
Most of times we do not face any problem after new theme and plugin installation but some plugins and themes requires high server requirement like high memory, mod_security, some extra php module so we need to check error_log and plugin requirement and then try to resolve this issue.