Leave copy of messages on server doesn't work [Outlook 2007]

In last two days, messages received in Outlook 2007 are being removed from server when opening Outlook 2007 on Desktop Machine even though leave copy on server is checked.
Laptop has same Outlook 2007 and using same comcast e-mail account and when I turn it on and open Outlook it downloads the messages from Comcast e-mail account and it leaves a copy on the Comcast server just fine.
All this started to happen also coincidentally after Comcast went to a new web mail platform called Smart Zone, so at first I thought that was the problem.
I changed the password on the e-mail account and then went and used laptop instead and it downloads the messages and it leaves a copy on the server. I see other people around the NET having some issues with leave a copy on server. Is this a corrupted file in my Outlook program on that particular PC?? does it have anything to do with XP Service Pack 3 update?
The laptop where Outlook 2007 leaves copy of message in server is running Windows Vista, while the Outlook 2007 that's removing the messages from server even though is set to leave a copy is running Windows XP SP3

 

Just to calrify; Outlook is set correctly to leave copy of messages in server. Not to remove after a certain number of days or any other option.
Our practice is to always leave a copy on the server and go directly into the server through webmail and delete what's not needed.
I did contact Comcast and we sent several test messages and they were arriving in Comcast' s server but were all being downloaded by Outlook and no copy ws being left on the server.
Turned that PC off and opened Outlook on laptop with identical settings on Outlook and test messages were being downloaded by Outlook and copy WAS BEING KEPT in server.
It seems that for some reason that Outlook is not working properly on the Desktop PC. The problem with uninstalling and reinstalling Outlook is that it retains all the settings and behavior usually remains after the reinstall.
Is almost like when Microsoft Word has a corrupt template and you uninstall it and reinstall it and the problem remains until you go into the Registry and delete the Template from the Registry.
How would I completely remove Outlook so it leaves no trace on the affected machine and then reinstall it and check if behavior continues??
I was also wondering if this would have to do with any of the Automatic Updates for Windows XP or Outlook 2007. The laptop has been turned off so it hasn't been updating since the end of December and it's running Windows Vista.