When it comes to tracing errors in Excel, there are a few things that you can do in order to make sure that you're able to find and correct them. First and foremost, you'll want to check the formulas that you have entered into your spreadsheet. This can be done by simply clicking on the cell in question and then hitting the F2 key. This will bring up the formula bar, which will show you the exact formula that is being used in that particular cell. If you see any errors in the formula, simply correct them and hit enter. You can also check for errors by using the Error Checking feature, which can be found under the Formulas tab on the ribbon. Simply click on this tab, and then click on Error Checking. This will bring up a dialog box that will allow you to step through each error one by one so that you can fix them.
Another thing to keep in mind when trying to trace errors is that they can sometimes be hidden behind other cells or objects. If you think that there may be an error hiding behind something, simply select the entire sheet by hitting Ctrl+A on your keyboard. This will cause everything on the sheet to be selected, and any hidden errors should become visible. Once you've found the error, simply fix it and deselect everything by hitting Ctrl+A again.
If all else fails, there's always the option of starting over from scratch. Sometimes it's just easier to delete everything and start from scratch than it is to try and figure out where an error is hiding. Of course, this isn't always an option if you've already put a lot of time and effort into your spreadsheet. In this case, it might be worth saving a copy of your spreadsheet before deleting everything so that you have something to fall back on if needed.