Situation: The ultimate frustration for many technicians is that even with a repair install and sometimes with a newly installed Windows, typically XP, but may happen in newer versions, will never complete the install from Windows/Microsoft Updates, or manual install. Most Common is version 1.0 and 1.1 and their respective Service Packs (SP), but has been known to happen with 2.0, 3.0, and 3.5. This can remain true even after using the .net cleanup tool to strip out all of the .net from windows before reinstalling it.
Solution: First give the installation some time to be sure the system isnt just being slow. The .net installs can take some time and may only seem to be hung. If you are sure its hung, open the Task Manager and sort processes by name. Look for MSIEXEC.EXE, there will be more than one. Now look at the two or more for the SYSTEM user. There will be one with a memory size of approximately 3,5XX to 3,6XX bytes in size. Right click the process of that size and end task...be careful not to end process tree. Within a few seconds the .net install will continue and soon finish. You may have to do this with each of the upgrades and SPs untill it layers in correctly to the current version.