Outlook 2007 “Not Responding”

Hello,

I need your help.
I am using Win 7 Ultimate on my Fujitsu Siemens Laptop and Outlook 2007.
Recently my Outlook is very slow to open and very very often it does not respond when I click on it (whatever the item I click on).
I have to close it by clicking on the X at the upper right corner.
It then offers three option, i.e. Find a solution and restart Or Restart Or Wait for it to respond.
It happenned before from time to time, but now it hapens all the time.
I’ve checked with Elevated Command Prompt SFC /SCANNOW and no conflict is found.
I have installed Microsoft Security Essentials, Ad-Aware for security.
From time to time I run Malwarebytes too.
Thank you in advance for your help.