Ajax error when installing
I had problem like this. You need to increase memory_limit.

For XAMPP: you can change it globaly in php.ini (in xampp located in '\xampp\php\php.ini')


  memory_limit = 8M // search for this "memory_limit" and adjust it by your needs (min 64M)


For WAMP: right click on the WAMP icon, then navigating to the PHP folder/menu-thingy and selecting php.ini, and find memory_limit (like on XAMPP)

After you made a change restart Apache and try to install Drupal from the beginning.