I placed a copy of the "Startup" folder on my desktop, and when I tried to delete it, I got error "Startup is a Windows System Folder and cannot be deleted". I tried to rename it to "l", but it is still recognized as a system folder. I have no clue on how to delete it.

I even tried a suggestion to open a command window, along with task manager, to navigate to my desktop in the command window, end the "explorer.exe" process in the task manager, and to type "DEL l" in the cmd. Even this did not do a thing.

Any suggestions?

First, try this;

http://support.microsoft.com/kb/308421/en-us