Hi,
Click Start, click Run, type sysdm.cpl, and then click OK.
Click the Advanced tab, click Performance, and then click Settings.
In Performance Options, click the Data Execution Prevention tab, and then click Add.
In the Open dialog box, locate and then click the notepad exe in the system 32 or suitebale folder where you are having that program.
Click Open, click Apply, and then click OK. When you are prompted to restart your computer, click OK. Then try to start NOtepad
If not,
I assume you are having problem in opening Notepad. If this is , then Try this link. I do not know what the OS you are having. Assuming that it is windows 7 , I give this link. Since 3 experts tried to fix this, try this with some care as advised in the solution. It would fix your problem.
But let me be specific in taking the back up the notepad.exe from the system folder, before attempting anything . Normally by changing the path, as copying to the desktop, would fix it if it is not a major issue.
http://www.howtogeek.com/howto/12617/how-to-replace-notepad-in-windows-7/ When taking control, you be specific to adopt all the ideas step by step. Even missing one advice may render the system not working. If any other replacement or workable solution is found, i will post then.