In the command prompt window, and from the bin subdirectory mentioned by gmchenry can you enter the command
splunk status
Does that say splunkd is in a Running or a Stopped state?
I had a similar problem some time ago whereby Splunkd had crashed, and so was in a stopped state, but it hadn't cleaned up all its child processes. This left at least one orphan process which maintained its association with port 8089. I think the root cause of my particular problem (SPL-86939) was fixed in 6.1.4.
It is also possible that a process totally unrelated to Splunk is also needing to use port 8089 and so the two are programs are conflicting over port 8089. If that's the case you'll need to change one of the programs to use a different port.
To find the process that is associated with a port you can use the netstat command
netstat -ano
This blog item may help you identify the process that is associated with the port (I've not tested the details in the blog item, and so can't comment on its validity).
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