@ayaz1 Read this thread here:

http://wordpress.org/support/topic/fatal-error-on-upgrade-4

I think that if you look at your server files you’ll see that no general-template.php file exists. So, what I would do is download a fresh copy of WP 3.3 . Rename or delete the wp-includes folder from your server files then upload to your server from your fresh  3.3 copy the wp-includes folder. 

However, make sure you read this thread as others have had the same problem as you. Your not alone.  Good luck.

This sounds like a problem caused by one of your plugins.
What you should try doing is going to your website using FTP, go into wp-content and rename your plugins folder to something else. Create a new folder and call it plugins. (this is an easy way to empty your plugins folder without losing all the files.)

You should now be able to login to your WP admin. Do so, and go to your plugin page. You will get a lot of messages saying your plugin was deactivated (this is good).

Finally, go back to your FTP and add your plugins again one by one until you find out which plugin has broken WordPress. I then suggest deleting it, or re-downloading the latest version of it.

I hope that helps!

Thanks Sam,

@samscholfield It did work but here is one more question from you is that, I have did a lot of work of seo in the back-end through all in one seo pack plugin.

Does that hurt my already work done regarding seo?

Please clear this as well. 

Thanks & Regards,

Ayaz

Regarding the seo plugin, your settings should have remained when you re-activate it. However I’m not too sure on that.I would also suggest completely removing the plugin that is breaking Wordpress.Double check the update section and make sure your installation is completely up to date.In future, always make a backup of all your files and your database before you upgrade, that way you can quickly revert and test the upgrade on a development version of your website.

@ayaz1 That’s great news. Glad it’s sorted!