What kind of icons?
If shortcuts, then see if the folders/programs still exist, or if they have been moved.
If not, and you're talking about certain types of files (check the extension) , then what type can't U open?
It may be a file association issue, (go to any folder> folder option >file types> open with, Or U can open the program U want and check the setting related to what files to open)
If not, U might have uninstalled something needed to open those types of files.
If this happened recent, then U can try a system restore from Start>run>msconfig>system restore
It may be a file coruption issue.
U might also have a virus. Just in case U can run a scan with Malwarebytes.