Sure, I can help you create a Line of Credit Calculator in Microsoft Excel. Here are the steps:

1. Open a new Excel spreadsheet and label the columns as follows: A1 - Loan Amount, B1 - Interest Rate, C1 - Start Date, D1 - Withdrawals, E1 - Payments, F1 - Current Balance.
2. Enter the loan amount in cell A2 and the fixed interest rate in cell B2.
3. In cell C2, enter the start date of the line of credit.
4. In cell D2, enter the first withdrawal from the line of credit.
5. In cell E2, enter the first payment made towards the line of credit.
6. In cell F2, enter the formula to calculate the current balance of the line of credit. The formula should be:
   Formula:

   =A2+((A2*(B2/12))*DATEDIF(C2,TODAY(),"m"))-SUM(D2:D2)+SUM(E2:E2) 

7. Copy the formula in cell F2 and paste it in the cells below to calculate the current balance for each month.
8. Enter any additional withdrawals or payments in the corresponding cells (D or E) for each month.
9. The current balance in cell F will automatically update based on the new withdrawals or payments.

That's it! You now have a Line of Credit Calculator in Microsoft Excel. Let me know if you have any questions or need further assistance.