Straight Line Depreciation using the IF Function (Excel '03)

Hey guys, first time poster but a fan of this website; its helped alot before.

However I find myself quite frazzled and here is my conundrum:
For school I have been trying to work out the Excel formula for straight line depreciation over a number of years. I will give the best description I can, here is my data and the cells it is in:
C61: 40,000 <-- This is the cost price/acquisition price of the item
C62: 5 000 <--- This is the residual value of the item i.e. its salvage value
C63: 5 <---- This is the expected life of the item in years

I am required to use the IF function to work out the straight line depreciation over the 5 years and then place it into a 10 year table. Obviously the item will depreciate at $7,000 a year and I did get my results to say this. However we must then be able to copy that formula into the 9 other years and have the depreciation stop after 5 years, as it has hit the salvage value. When I copied my formula it continued the depreciation for the full 10 years, not just the 5 years it was meant to (ie. If i had a list of cells from 1-10 which represented the Life Years of the item, after 5 years the formula should give me 0 amounts as the item has depreciated to $5,000 and would have been sold or disposed). After this I must then also test the formula by changing the expected years of the item, say from 5 to 6, and then it should give me an updated yearly depreciation for 6 years and then starts saying 0 after 6 years as it has reached its salvage value

Please attach a copy of the worksheet

Here is a copy of the worksheet

I tried to formula
=IF(AND(C4<>0,C5<>0,C6<>0),SLN(C4,C5,C6),"") and this worked for the first year but then stopped working because when i copied it to another cell it turned to C5, C6, C7