Text tab

I installed WordPress 3.5 through my web hosting provider and now my text and visual tabs are not working. What do I need to do to fix it. I am a beginner at this at this, so step by sep answers would be greatly appreciated.

Thanks

p.s. I’ve tried to clean cookies, restart browser, uninstall themes, use original theme (Twenty Twelve) and none of these worked. I’ve even tried to add WYSISYG tab plugins and they did not work either.