Old deleted form still running at startup vb.net

I'm new to vb.net and need some help.

I'm not sure what's happening but a deleted main form loads on start up even after setting a new form as start up.

I took a few buttons and copied it on a group container and named it Dial Pad on the old form. After testing to see if it works I adjusted the dimensions and ran again but this time it stayed the same. I clicked on the buttons but nothing happened. Check the code and there was code in it and correct. However there seem to be other set of buttons name as same but with a 1 at end.

I checked the solution explorer and it didn't show, only the originals showed. After frustration I created a new form and copying the code and created new controls. I deleted the old problematic form and set the new one as start up but the old form with the dial pad still appears and only exit button I added and coded works. The datagridview on old forms works as well and is the old way I can get to the other forms which still work.

This problem sometimes indeed occurs. The solution is pretty simple. Go in the menu to Build > Clean Solution and rebuild. Or else, open the context menu on the solution node and select Clean Solution.

Screenshot of the menu:

Screenshot of the solution node context menu: