We are sorry about the issue you are facing with Lightroom 3.
Would you mind sharing the operating system and other general specifications of the computer you have installed the application on? Does the application crash while performing a task or are the crashes random? Do you get any message or crash report?
You can disable the Graphic Processor from the preferences of Lightroom by going to Preferences, then select OFF from the drop down to Use Graphics Processor and relaunch Lightroom to check if that helps.