Assigning a domain user to run MSSQLSERVER service 2008R2
If you check the event log, does the event say something about needing "log on as service" rights?

In my experience you will need to add 'log on as service' rights to the account you select. Although the SQL Server Configuration Manager is supposed to handle this, I've found that it does not always. Try the following:


Log on to your domain controller and load the group policy management console (depending on your AD version)
add 'log on as a service' to the account you created for the SQL Server service in an existing or new group policy object. (maybe ask a sysadmin to assign this right for you)
Load SQL Server configuration manager and set the service account to the account you created