Did you happen to update to Internet Explorer 9 recently? There have been a large number of complaints recently. Also if you remember when was the last time that it was working? Did you install anything since then?
Actually I've researched it and found a person that figured out the issue that he was having almost just like this issue. Here is what he said...
Here's how to fix this problem with IE 8 and Vista.
Microsoft will tell you that you need a hotfix installed on your exchange server, this is NOT TRUE!
Here is what you need to do:
Click "Tools" in the menu bar
Select "Internet Options"
Click Advanced settings tab
Click the "reset" button at the bottom of the advanced settings menu
Close Internet Explorer after the settings reset
On the IE 8 welcome page, click next
Select "do no turn on suggested sites", click next
Select "choose custom settings", click next
Chose your search provider, click next
Select "I don't want updates for search", click next
Select "Turn off all accelerators", click next
Select "Turn off smart screen filter", click next
Choose default browser, click next
Select "yes" for use compatability view updates
Then when you go to your Outlook Web Access account, Internet Explorer will ask you if you want to install the "MIME Edit binary behaviuor" add-on. DO NOT INSTALL THIS ADD-ON!!!
This is the add-on that is causing all of your problems, and it can not be properly disabled with the add-on manager. Internet explorer will ask you if you want to install the add-on every time you open outlook web access, and if you install this add-on, you will have to repeat this entire process to get your email working properly again!
Let me know if this fixes your issue if not I'll check for another method for you.
Thanks for your reply , however it did not worked in this case......eventualy I had to stop the services using msconfig.exe and found out that a service named ScanQuery (that some are defining it as a malware ) has benn the couse for those crashes ......I found over the the Internet how to remove it and ...happy ending !!! All is back to normal.