You can simply run one of the below query to check the SQL Server last restart time.
SELECT Dateadd(s, ( ( -1 ) * ( osd.[ms_ticks] / 1000 ) ), Getdate()) AS serverrestartdatetime, osd.sqlserver_start_time FROM sys.[dm_os_sys_info] osd; OR SELECT name, crdate FROM sys.sysdatabases WHERE name = 'tempdb'