I got 0 page rank and 0 back links on google.com when I woke up today morning.

What should I do?

Have you done anything that you shouldnt have?? hidden keywords, cloaked pages, or black hat stuff?

It could be that it is just temporary and your site will be back with the next spidering of your site. (if your site was down when it was spidered last)

If you didnt play by the Almighty Google rules then you will have to remove anything you did to offend them and then send google an email explaining the errors of your ways and they will hopefully reindex your site.

Don't expect a reply or try to give excuses. "THEY" know better.

Otherwise, after you remove the offending content or code, it will prob be about 3-6 months and you will be back.

Take a look at these links or more help

http://www.google.com/webmasters/2a.html

http://seopapers.com/article/281

http://www.pandia.com/features/banned.html

Good Luck

Same reply as in item 1/ in this thread

http://www.webmaster-talk.com/showthread.php?t=37871

Sit tight - have a drink - don't panic.

It doesn't seem unusual for a site to become "invisible" for a while during an update. Got a few "missing in action" myself at the moment but have faith that they will be back.

How's traffic?

A site which was banned was given to me, and by cleaning all the SEO out of the code and writting a simple email to google requesting they place it back online works. 1 week later the site was online with a page rank of 3 somehow.
Its is simple and quick to get your site back online if you have been banned. I think they will only put you back once though. You get banned again and thats it for that URL name.
To check if you have been banned type this into Google
site:www.mysite.com
If there is no result then you are banned

one of my sites ist banned from August 05, 0PR, 0 back links, but Googlebot visiting sometimes, I have emailed to google several times and nothing.

Good advice. Wait a while if nothing happens email them

I got 0 page rank and 0 back links on google.com when I woke up today morning.

What should I do?

try getting back to sleep....lol
ok, serious now.. what page rank did you have before? could it be a temporarry problem in google?

IMO you should redesign existing pages to make use of CSS and you should change your title tag to include your website/company name, and usually the title of the current webpage where content is present. I think to get good page ranking and rating you need to take care about SEO for your site.