After reboot SQL Server service won't start automatically if tempdb located on the RAM disk. I think it is because it starts before the disk is ready. Disk is configured to start at boot time. Are there are any solutions?
Does it produce any error messages in the Windows event log?
Perhaps changing the MSSQL Service startup type from Automatic to Automatic (Delayed Start) in Services.msc can do the trick. This would cause the server to start a bit later after all automatic services have started, at which point the RAM Disk should be available.