Just used those instructions on Windows 7, with JDK 1.7u55, and Jetty Distribution 9.2.0.v20140526
The logs in C:\opt\logs\ should show the logs from both prunsrv and Jetty.
(In fact, there are usually 3 log files generated)
C:\opt\logs\%SERVICE_NAME%.yyyy-mm-dd.log
C:\opt\logs\%SERVICE_NAME%-stderr.yyyy-mm-dd.log
C:\opt\logs\%SERVICE_NAME%-stdout.yyyy-mm-dd.log
Since you indicated startup crash, here's your troubleshooting guide...
1) Check the administrative event logs
If there is an error here, address it, as prunsrv itself couldn't run
2) Check your prunsrv logs - C:\opt\logs\%SERVICE_NAME%.yyyy-mm-dd.log
If there is an error here, its likely you have your prunsrv configuration off/broken.
uninstall the service, fix the configuration, install service, test, lather, rinse, repeat.
3) Check your stderr logs - C:\opt\logs\%SERVICE_NAME%-stderr.yyyy-mm-dd.log
If there is an error here, its a jetty base configuration issue.
4) Check your stdout logs - C:\opt\logs\%SERVICE_NAME%-stdout.yyyy-mm-dd.log
If there is an error here, its your webapp's issue.