Depreciation of fixed asset

I'm trying to calculate the Depreciation of the fixed asset for some items
I've tried the formulas that came with Excel but i don't know its not working or not give the correct value
so I attached a file as an example
what I'm trying to have is
1- straight line method along the asset life
2- salvage must be ( 1 )
3- if the purchase date is equal to or before the middle of the month (14-15/02/2004) so the start of depreciation have to start from the beginning of the current month ( Feb) but if the date excess the day 15 ( 16/02/2004) the middle of the month , the the depreciation must start from the next month.
so any one can help ?