follow this guide from start to end You may find that a few thing I am recommending to delete are already deleted from your computer so skip those steps.   1 Use Microsoft's Installer :  This step is crucial as Microsoft's uninstaller disables the services as well. Choose SupportAssist and uninstall, Uninstall Dell updates by running the the uninstaller again. If Support Assist doesn't show in List ignore this step.  Reboot (important)  C:/ Program Data/ PCDR  C:/ Program Data/Supportassist  C:/ Program Data/Dell/Dell data volt  C:/ Program Files/ Dell/Supportassist  C:/ Program Files/ Dell/ Dell data Volt  C:/ windows/Temp (everything inside the folder  Remove these Registries  Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services key. Delete Dell hardware service, Delete Dell client management service, Delete Dell updates.  Open device manager > system devices : If you see 2 Dell dala volt devices, please uninstall the second one.    last step : Download dot net  [URL] if it's already installed, installer will give you option to repair or remove, choose remove and reboot.  Install again.  Reboot  install SupportAssist 
Anybody can advise, that the Dell support assist has failed to install on my Inspiron 7306 laptop and is showing Installation failed. Please reboot your PC and try again." I did but the same result...
Dell Support Assist Installation always failed