if plesk is not running and you see in /tmp/autoinstaller3.log this:
Package matching php-5.3.3-3.el6_2.5.i686 already installed. Checking for update.
Running rpm_check_debug
Exception: Scriptlet or other non-fatal errors occurred during transaction.
ERROR: Failed to run the Yum utility.
The Yum utility failed to install the required packages.
Attention! Your software might be inoperable.
Please, contact product technical support.
then you have to update php by hand yum update php
then to run /usr/local/psa/admin/bin/autoinstaller --upgrade-installed-components --select-release-current
wich will upgrade installed components (as auto upgrade option in plesk does automatically) and plesk interface will start again.