Excel 2003

Part 1:

From the menu: Insert = Name = Defined:

N =10
O =20
M =30

Spreadsheet cell K3 displays N.
Spreadsheet cell K4 displays O.
Spreadsheet cell K5 displays M.

Ive tried: =SUM(N+O+M) displays 60.
And =K3 displays N.
And =sum(K3+K4+K5) displays error #Value

In cell L10 for example, how do I add cells K3 + K4 + K5 such that in L10 is
displayed the number 60?

Part 2:

User inputs first number directly into spreadsheet, example range 1 to 10,
into cell B39.
Cell B40 then needs to check: If B39 < 10 then B40 = B39 + 1
Else B40 = 1

Hows the syntax work for this If statement setup?