This problem arises when the system runs some system optimization software or is infected with a virus.
If just individual programs disappear, you can choose to fix this problem manually. First find the running file of the specific program, create a shortcut, and then paste it under the path of "C:\Documents and Settings\All Users\Start Menu\Programs".
If almost all programs disappear, but you can find them running correctly in the Start search box, it is probably because related folders are hidden.
Please enter the address of "C:\ProgramData\Microsoft\Windows\Start Menu" in the Address Bar and press Enter.
Right click the blank space of the window, and then click "Property".
On the "General" tab, check if the "Hide" property is selected or not. If selected, please unselect this property, and then click "OK".
(If the permission confirmation window pops up, please enter your administrator account name and password, or click "Continue")
PS: If even the "All Programs" disappear, you can check the configuration status of the items related to the group policies to try to resolve this problem.
If the methods above still cannot resolve the problem, finally we can also restore the system or use the installation disc to repair the system.
If it does not work all the same, you are suggested to dig the Forum to see if any solution can be best for you.