It could actually be a lot of things that causes your world editor not to start.
For example: faulty registry keys can cause applications to hang. (Use something like Ccleaner to find out) Like spartipillo mentioned...
Windows Services might block applications and cause them to hang. (Right mouseclick on computer -> manage -> Services and applications -> Services)
Shut down all non windows services one by one to find out which one is causing this.
(I personally think this is your problem, some kind of newly installed application which has some service blocks your worldeditor121.exe from working...)
Corrupt hard disk sectors as mentioned before can cause lots and lots of problems. (I can explain why, but that would cause this post to become massive...)
Faulty RAM can cause your computer to become incapable of doing the simplest tasks. (Because there is too less Random Access Memory to access several applications at once)
Are you experiencing any other issues on your windows machine besides the world editor or is it the world editor specifically?
Reinstalling didn't work?
What processor architecture do you have?
Is it 64 bit or 32 bit? (shouldn't make that much of a difference though)
Got administrator priviliges?
Tried compatibillity mode?
Have you done a full virus scan in case of infection in windows safe mode using MBAM?
If you find the error code in the windows logs from the application crash of worldedit121.exe let me know. (Right mouseclick on computer -> manage -> Log files -> Windows log files -> applications)