Running Cubase 5 and difficulties on using it with computer

I saved a project few days ago with this software. I wasn’t able to use my computer for at least 2 days. I did not check my projects since then. I tried to launch my saved project and it showed me message “'missing plugins.” Can you tell me why this happened to Cubase 5? What could be the possible cause of this problem? Can you provide me instructions on how to resolve it? Can you give me alternative ways on how to eliminate the problem?
Thank you!
