Get a new site and stop spamming it with forum signature links, that would be a good move.

One solution can be like make you site more strong by popularizing it through creating contents on sites like squidoo, hubpages, ezinearticles etc. The more the popularity more will be the chances of getting high rankings in search results.

Start a new site, but i'd keep using forum links. Just don't blast them x-rumer style and you should be fine.

Heck, if your old site has pr just 301 redirect it at your new site, problem solved!

Were your anchor text and backlinks diversified?

First of all you need to understand whether your website is penalized because of panda or penguin based on that you need to take the decision. If it is panda then it is because of content,so try to create unique content for each of the job post or else if it penguin then cross the back links webmaster tools and remove all the low quality back links using disallow option. There is not wrong is working on the existing site once you fix the issue based on the two points that i have mentioned.

Try to develop and promote a new website. After that Get DMCA certification for your website. So, even if they copy your website then it won't get affected by Google algorithm updates.

Its May Be Due To An Update In Google Rules Or Google Dance. You Should Focus On Quality Of Work And Use The Unique Content. It Will Help You To Get the Website Back In Rank.

May be you will find your answer from this post Signs Of A Google Update? May 7, 2013

There is an update or upcoming update due to which your site has gone down.Try to make your site more search engine popular.

Your site needs authority. If you spammed CNN.com with 5,000 forum profile links, do you think it would affect their rankings?

NO.

So the key is to build authority backlinks, not mass produced spam crap. Either build them yourself manually or with a legit software like SEnuke.

Please avoid the cheap blasted spam links. These guys could care less about your business and they will make Google dislike your website.

Focus on websites with HUGE authority. My clients get links from Wordpress, Huff Post and .EDU websites. Links that Google thinks "Wow. If Huff Post links to you, then your website must be awesome. Here's some more traffic, pal."

That's the secret to success and the faster you start building these links, the quicker you will get more traffic in the SERPS.

Also, cover the basics of On-Site optimization and a faster loading site!

The site in question is Job Vacancies and Career, Business Ideas and Scholarships - and not the one in my signature. I have since abandoned that one and concentrate on the main one.

You may be hit by the penguin update, No Anchor diversification and low quality links may be the cause of sudden fall.

The advice in here is all over the place so let me try to give you a course of action:

1. Remove all the crappy links you can.
2. Improve site structure
3. Add quality content
4. Get 50-100 strongly related links
5. Let the site age, dont do anything for 90 days

Everything has been changed after PANDA/ PENGUIN so try to forget what you got!!
Now concentrate on making new site with quality backlinks and good contents ofcourse. Less backlinks can be helpful but it should be quality backlinks. Browse this forum for latest methods of SEO.
Good Luck !!!

As this is going in multiple directions - thought I'd add mine...

I'd stop worrying about all the tricks and just focus on providing valued unique content to your target market on a consistent basis. All of Google's screwing around is to try to help their searchers find the best quality content...so focus your energies on providing the best quality content and a) you'll have happy customers and b) Google will kiss your...

Wouldn't that be nice for a change?

forum signatures work well for me. just focus on relevancy.