Check with these options:
1) Either rename/remove Plugins folder via FTP or disables all the Plugins from database
2. If you have an access of PHP.INI file of the account/server then change the line in PHP.ini where line shows 32M to 64M:
memory_limit = 64M; Maximum amount of memory a script may consume (64MB)
3. If you do not have access of PHP.ini file then add this to an .htaccess file of your domain:
php_value memory_limit 64M
4. Try to add this line to your wp-config.php file to increase allocated memory to PHP:
If all this option can not resolve the issue then you need to contact your hosting service provider to resolve this issue.
Also change the memory according to your requirement.