I have a problem adding a custom option to product. When I click on the "Add New Option" button nothing happens? And I have no clue why its happening. Any help would be highly appreciated.
I've just had the same issue, I found that disabling modules one by one until the custom option could be added worked.
For me it turned out to be Magecomp Absolute Pricing that was causing the issue.
If there are any try to figure out what causes the problem - you could then try to disable all custom/community modules one after the other. Disable the cache when trying that.
Also, it could help to reinstall the Core Modules through Magento Connect - you should only do that if you're really sure you haven't modified any core files (Core, template, translation, etc files) since this will overwrite the complete kernel.