Windows Service in C# that Imports from Excel and Dumps data

I need a Windows Service Application, which has timer in it, which checks a folder after 12 hours, and opens all the excel files which are Marked UNUSED, and dumps the data into a table in SQL Server 2005 and then edits the name of the excel file to USED. Continues to do it on daily basis.Kindly help me out to make this entire service.. Thanks..