You could turn off the Size column, by right-clicking on the header and unticking it.
The calculation of the size of all the components on the disk can take quite some time.
If this does not help, and only if you have lots of installed programs, or if you have installed and uninstalled programs many times in the past, then it might be time for registry cleanup and reorganization.
My personal favorite products here are Eusing Free Registry Cleaner and Eusing Free Registry Defrag. But take good backups before starting, and especially a system restore point.