About to give up... any help

for some reason after the panda update all my numbers one spots for all my sites vanished overnight. My main site which had been number one for about 3 months and 2-4 for over a year suddenly moved to the bottom of page one and then two and now its been on page 10 since then. After the update I stopped building links for a while because everytime I did it seemed to push it off the results but when it came back it came back worse. This month i've come back to it and started building steady links But 20 days later i get it jump to 500 back to 100 and so forth.

at the same time ive been targeting one of my other sites and nothing seems to be touching them. I used to build just forum profile links but now i've been writing articles and posting them on web 2.0 sites and getting links to them and bookmarking etc..

For my main keyword some of the sites on the first page have like 15 incoming links. I have around 6k.

While my sites are still indexed. I'm wondering if google has put some sort of penality on my domain or server IP.

I'm really not sure how to move forward, i left my job back in march to focus on my business becaue it had gone so well 8 months prior. If I cant turn things around in the next few months it looks like I'm back in the job queue.

Any advise from people who have had similar issues are welcome.