This is hard to answer without any info on your model computer and operating system. Try using System Restore to go back to a few days ago.
well I don't know what I did , but I did a disk clean up and at the end i opted delete and now when I go  and try to open a file a get an error box with a big red X and all it says is class not registered. can some one help me understand this and how do I get it back to where i could open files...thanks...
class not registered