Hi Kim,
Sorry your having issues. Can you attach or email me the log files from the location C:\users\ki496595a\AppData\Local\Temp\sapinst_exe.1224.1462374604? This should provide some clue as to why the sapinst isn't starting.
Regarding the host agent, you can uninstall it and just install the Diagnostic Agent as it includes the SAP Host Agent 7.21
Also, are you running this install as a local administrator? What operating system?
Regards
Toby