Heavy Drop in Alexa Rank & Google PR Caused by 404 errors?

[Vijay]

I am running a website for past 3 years. http://www.wwelivetv.com
At February 2013, my alexa rank was close to 145,000. But all of a sudden my rank dropped to 1,542,204 (May 2013).
My page rank dropped from 3 to 1.

Generally i used to get around 1.5k visits per day, but now it dropped to 700 visitors per day.
I don't know the actual reason behind the rank drop.
I am running a sport site so i update it regularly (at least 2 post per day)
I am using Wordpress. All In One SEO Plugin

I have installed a forum section (on feb 2013) using subdomain as forums.wwelivetv.com.
But I have used that for only 15 days and then removed it completely because many people begins to spam the forum section.

Then i got a message from google webmaster tools as,
""http://www.wwelivetv.com/: Increase in not found errors"
"Google detected a significant increase in the number of URLs that return a 404 (Page Not Found) error. Investigating these errors and fixing them where appropriate ensures that Google can successfully crawl your site's pages. ""

I think the 404 errors caused by the removal of forum section caused me this problem of alexa and page rank drop.

CAN ANYBODY HELP ME TO RESOLVE THIS PROBLEM

[Matt]

Maybe your website hi by a Google algo update.. 404 errors are not the reason of your dropped ranking and alexa. there are ton of articles out there about 404 errors.Not really these errors effect the website ranking. Post your problem on google official product forum. this can help you!

[ABC]

You know the problem and you know the ans as well.

Collect all your 404 page and block it.

also include the forum site url in robot.txt file and upload in GWT which will block all the url from indexing. hence no penalty and recover rankings.

[robert m]

make sure there are no broken link to the forum page - the links are probably throwing up the 404 error