What I have found is that when you install QV server, it asks for the account name in the format domain\accountname, but if the service stops running and you browse for the account as in my point 2, the account name appears in the format firstname.lastname@example.org. I'm not sure what difference this makes, try both to see which works for you.
When you change the account settings make sure you stop and restart the service to check that the account can log on.
Also, on the Recovery tab of the service properties, set First Failure, Second Failure and Subsequent Failures to "Restart the Service", for all five of the QlikView services. That ended a lot of the problems I was having with keeping the services running.