I never had that type of problem with Dead space 2. Are you sure that there are no stability problem with your pc, or and hard-drive problem. In any event, if you reinstall Dead Space 2, in order to not use an activation, you should use the de-authorize tool ( http://activate.ea.com/deauthorize/ ) before re-installing the game, or totally de-install the game before going thru with another installation, even if it's on the same computer.
You could try this:
1- Backup your saved games ( documents\EA Games\Dead Space 2 )
2- Uninstall Dead Space 2
3- Re-install and activate the game. ( I would probably re-download the game, just in case there was some corrupted files which weren't detected during last install )
