Firstly you mention new RAM as well. Take it out. The thing to do is check each component seperatly. Try without the memory and see if its ok, if it is you know its the memory. Then post back if its still locking up as you will probably need to delete the drivers are reinstall. Will need more info if you post back. operating system, how much memory, what card you had and what card you have now plus dis you delete the drivers for the old card before you switched off and plugged in the new one.