If Respondus 4 is crashing when you attempt even simple things (eg., opening a file, adding a question) it’s possible that the installation has become corrupted. Program files can be corrupted when other programs are installed, when a computer has a bad crash, and for a variety of other reasons.
Once you have confirmed that the computer is free of viruses and spyware, try reinstalling Respondus 4 to your computer. If your institution has a campus license, obtain the most recent installation program from the contact person at your institution. If you have a single-user license of Respondus 4 you can download the current installation program from the Respondus website.
Go ahead and reinstall over the existing copy of Respondus 4 (there's no need to uninstall it first). During a reinstallation, you won't have to worry about entering activation passwords since this information will be detected from your earlier installation. You also don't have to worry about your existing project files (your exam files) because they are stored in a folder that won't be affected by a reinstallation.