Using Office 2007 Excel

Usually I highlight the column and press the SUM icon where
I want the total to be placed. However, there seems to be a
previous formula within the column, as the incorrect total
appears!

Several of the cells in the column of figures seem to have a
filled in triangle at the top left-hand corner (for some reason
unknown to myself)! The total I get bears no resemblance to
the figure it should be.

Is there any way to remove a possible previous formula please?
Or can anyone offer advice? Other totals within the worksheet
seem to be alright.

Thank you


--
Frankie