Based on the error that you provided it sounds like the account that you are using to start the splunkd forwarder process most likely does not have the necessary level of permissions to start Splunk as a service. I would suggest checking windows services.msc and either update the account by re-entering the password(if it is incorrect), use an account with a higher permission level, or use a local system account(which is the default if you didn't specify an account when installing).
Well thanks for the suggestions. I just solved my own question.
I solved the Splunk issue which had the following error when I tried to start the SplunkForwarder service.
"Windows could not start the SplunkForwarder service on Local Computer. Error 1069: The service did not start due to a logon failure."
I fixed this error under the SplunkForwarder service properties. Under the Log On tab, I deselected the default radio button for “This account” and its accompanying “tis\splunk” user name and password and selected the radio button for “Local System account” and no box checked for “Allow service to interact with desktop.” Now the SplunkForwarder service starts OK with no errors.
Similar issue at Error 1069 when starting splunkd using domain account
@ttchorz concluded by saying
-- ... I ended up creating a new user with different password and using that account to solve this problem.