After restart the tempdb file has defaulted to the size it was last modified to. In this case you need to shrink the tempdb data files.
USE [Tempdb]
GO
DBCC SHRINKFILE (N'Tempdev', TRUNCATEONLY)
GO
If this does not works try simple shrink
USE [Tempdb]
GO
DBCC SHRINKFILE (N'Tempdev')
GO