Vista - Excel 2007 problems

I have used Excel on older machines for many years without problems. Today I compiled a spreadsheet with columns I totalled using the sum formula. That was ok. I then went to sheet 2 and compiled a much more detailed and longer spreadsheet. On this sheet I then tried to increase the decimal points and it did not respond. I tried the formula for the addition of columns and it did not respond. The total box stayed showing the formula but not the total sum. The digits remained without the extra decimal points.It seems as though it has a nil response to commands.
I have Excel 2007 and Vista Home Premium. Obviously I am doing something stupid but I cannot fathom what. I was familiar with the older excel and thought this would be the same but obviously it isn't. Help please?

Hello Jean & welcome,
Have a browse through the link below & see if it helps.

Microsoft Excel 2007 Tutorial—Free & Online


Please let us know how you go.

Is workbook calculation set to automatic in excel 2007? Go to the start/orb/horrible replacement for the file menu and go to excel options, then the formulas tab. Ensure automatic is set for workbook calculation.

Edit: Also F9 will recalculate any cells that are linked to values of other cells.

Edit #2: I reread what you wrote again, and in case I missed the point (or this could entirely miss the point), make sure you right click the cells which aren't displaying the decimals properly, going to format cells, the first tab number, and choosing an appropriate formatting option for your numbers.