What can I do to stop the duplicated value in a specific column or row, and if I entered a duplicated value it opens an alert window message?

from the data tab select data validation customize your settings according to your rules and the message you want to add as an alert or a forcing and stopping window etc...

I think you should go to Data tap then select Data Validation.

1- Select Data - column and row -

2- Choose the data list

3- Click on Data Validation Option

4- Select option - Data validation -

the best fit solution for this situation is Data Validation.

follow this steps:

1. select all the cells you want the validation to apply to.
2. go to Data tab > Data tools group > Data validation command
3. in the Data validation dialog box choose Custom from Allow combo box.
4. in the Formula box write the formula suppose your data is the range E1:E5 : =COUNTIF($E$1:$E$5,$E$1:$E$5)=0
5. in the Data Validation dialog box go to Error Alert tab. And write you alert message
6. done

hope this answer your question