Ok so when ever i try to launch New Vegas, steam now gives me an Error saying "Error 51" i tried validating my files didn't work. I use Avast anti virus and people say its because of that so i tried disabling it for a little while but it still gave me the error. I tried telling avast to ignore Fallout New Vegas folders/files but it still gives me that. Any ideas why this is happening?

Did you read this article Rose?  It might help if not:

https://support.steampowered.com/kb_article.php?ref=2235-YXVB-8261

Also this might apply to you as well:

http://forums.bethsoft.com/topic/1348070-windows7-quad-core-fixes/

I did read the first one, didn't help.
I read the 2nd one and that didn't help either. :\

Hm... I'm not sure then.

If it worked fine before, you probably need to ask yourself "what have I changed about my PC between then and now?" I've solved a lot of problems that way.

I think I had that issue when I tried to play Morrowind once. I just restarted my computer, and it started working again.

Restart Steam (Using Task Manager or otherwise) Trust me  

Tesvixen wrote:

Hm... I'm not sure then.  

If it worked fine before, you probably need to ask yourself "what have I changed about my PC between then and now?"  I've solved a lot of problems that way.

WHOA ! I'm wishing I knew about the disable-intro tweak, a long time ago ! Modding would have been much-less tedious, but, at least, it still can be.

EDIT:
Oh poop. It worked one time for me. Can't get it to do it, anymore. Darn..

I restarted my PC it fixed it thanks alot everyone

Glad to hear it Rose.