You need to resolve the actual issue; switching the mode to 777 to start MySQL will not help anything as then it simply starts with default settings, which does not help you.
The log was initially complaining about your ib_logfile* size being different. So just do the following:
1. Stop MySQL
2. chmod /etc/my.cnf to 644
3. Move the ib_logfile* files from your data directory to another location for safe keeping.
4. Start MySQL as root or using sudo
That will force MySQL to re-create your ib_logfiles as the new size to fix the issue.
After you do all of that, please post up the error log again if it still does not start.
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Scott Nemes
MySQL DBA
http://www.linkedin.com/in/scottnemes
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