[support] how to reset the visit counter? always 125 visitors online!

[Simone Dal Maso]

Hi,
I have a serious problem with my d6.15, because yesterday our service 
provider made some strange things with date, they installed a plesk update 
that caused problems to many users.
In particular, my problem is that the drupal counter is always showing me 
that there are 125/140 anonymous visitors, that is simply impossible!
and, cron doesn't start any more, I have poorman's cron module, and I must 
run cron.php in order to run it properly.
Any hint on how reset the visit counter?
I tried to clean the cache, to put website in offline mode and then online, 
run update.php, nothing1 always 130 visitors!