Hi there! I'm sorry to hear that you're having trouble with the Design Mode button in Excel. Here are a few things you can try to get it working again:

1. Make sure you're in the right view: Design Mode is only available in certain views, such as the Developer tab or the Design tab. If you're not in one of these views, the button will be greyed out. To switch to the Developer tab, go to File Options Customize Ribbon, and then check the box next to Developer in the right-hand column. If you're already in the Developer tab, try switching to the Design tab to see if the button becomes available.
   
2. Check your security settings: Excel has some security settings that can prevent certain features from working properly. To check your settings, go to File Options Trust Center Trust Center Settings, and then click on Macro Settings. Make sure that the option for "Disable all macros with notification" is selected. If it's set to "Disable all macros without notification," this could be preventing Design Mode from working.
   
3. Check for ActiveX controls: Design Mode is often used for working with ActiveX controls, such as buttons or text boxes. If you have an ActiveX control on your worksheet that is not properly registered, this could be causing the Design Mode button to be greyed out. To check for ActiveX controls, go to the Developer tab and click on the Design Mode button. If you see any controls with a red X over them, this means they are not properly registered. Try deleting them and then re-adding them to see if this fixes the issue.

I hope one of these solutions works for you!