Some viruses now are messing with your file associations making it hard to open programs, such as your Web browser so that you can download and install an anti-mailware program, or even open the cleaner application itself. It's usually simple to remove the changes made when in a registry editor, but since Regedit.exe and other editors are executable files, you can't easily open them either!
Below is a registry fix that I have found useful to have on hand to easily reset the .EXE file association back to it's normal state so that you are no longer prevented from running programs.
Repair EXE Registration.reg
Windows Registry Editor Version 5.00
Importing this registry data file will remove any custom edits that any malware makes to your .EXE file associations in the HKCU area and then sets the file association open command back to normal. From there you should be able to open your malware cleaning tools.
We recommend that you copy the registry data file to a local disk on your computer prior to running due to the fact that newer versions of Windows will often by default not allow you to import a .REG file if you run it from a network share.