why cannot install robohelp again

Use the http://www.revouninstaller.com/ that Mr. Grainge recommends. I have battled getting RoboHelp 7 installed for days. The support center at Adobe was pretty useless - the second tier person that I spoke with could only recommend blowing the entire system away.

I tried the Revo Uninstaller he recommends and was able to install and use RoboHelp within 5 minutes. I wish I had found this thread days ago.

Thanks for the information.

Welcome to the forum.

Does RH appear in the list of programs in Add / Remove? If it does, then try uninstalling there.

If not, do you have a System Restore Point to return the registry to where it was before you started the installation? Always wise to create one first. After you have rebuilt a few PCs because you didn't, you soon remember that stage.

Beyond that, you could try http://www.revouninstaller.com Not tried personally but someone did report good results. If you are unsure about using such a program which does edit the registry, go cautiously and get expert help. Do you work with developers? Get them to help if you can or someone like that. Don't be too daunted if you don't have such help as I think RevoUninstaller creates a System Restore Point so that you can get back to where you are now. (At least you will be no worse off)