What should i do my antivirus has paralyzed my computer?

Wow, seems like something took ahold of your antivirus to make it go haywire. Now what you should do is immediately get rid of the antivirus (dont worry, we'll resolve this later). Try to run your computer in safe mode and uninstall it from there. If it still wont let you use anything there, download a portable OS like Ubuntu and run it in your computer. DONT install it. From there, I doubt your antivirus will reach you through a different OS and so you should be able to uninstall and/or delete the files for it there. Once you do, close everything and start your computer as always. Make sure its gone and if it is, I suggest you download Microsoft Security Essentials for now. At least that antivirus wont annoy you to get any full version programs since its already full itself and its a good protection. Of course this is my opinion so if you dont like it, feel free to install bitdefender again if it worked out for you. Good Luck.