Problem with users and sessions on Magento frontend

Question

I have a problem that is driving me crazy , I'm completely lost. With my limited knowledge I think is a problem of sessions, but really have no idea how to approach it. This is the problem:

Users can not enter their accounts through the frontend. When they try to sign in, the page just refreshes but not enter, on your own account or through Facebook . The system will not show any errors or anything , just do not walk , so the reaction is the same when you put the correct data or when you put the wrong key on purpose , just refresh and nothing else. If you create a new user you can get in, but if you come back later you can not enter anymore, you'd have to go create a new user again.

Now comes the strangest :
If is given the case you are a new user, you have created an account and get to order , such order appears in the admin with a dummy user that I created a few days ago . That is, last clients, each one different , besides not receive any order confirmation email , their orders appear to me on the panel with my dummy user data , only the email of the client is correct, although them of course when ordering have entered their data. I have to say that I removed yesterday the dummy user but still appears.

Answer 1

Even if this sounds like it's too broad and does not have a version specified, I will take a shot in the dark and assume that your version 1.8.1 and you are using a theme for an older version.
A lot has changed on 1.8.1 and the themes for 1.7 (even 1.8.0) are not compatible anymore.
if you take a look here in the loginPostAction you will see this code:

if (!$this->_validateFormKey()) {
    $this->_redirect('*/*/');
    return;
}

This is new. It validates the form key for additional security. If you don't send a form key you get redirected to the login page without any errors showing.
For test purposes comment the lines I mentioned. If it works then ... bingo....that's your problem.
Uncomment the lines again and make your login form 1.8.1 compatible by adding this code inside the <form> tag in your login template.

<?php echo $this->getBlockHtml('formkey'); ?>

If my shot in the dark was a miss, and you don't use 1.8.1 tell me and I will delete the answer.

Answer 2

I had this issues some time a go. I have tried storing session in redis, then memcache, then files. For my magento only files was ok and somtime even that was not enough and magento falls on storing session on db. Now i have files, folder is with correct permissions and i have a cron for deleting sessions older then 24h. This is how i have managed to bybass this issue