Can't open scripts with monodevelop?

Hi, I’m new to unity. in fact, I’m new to any game-developping at all. my problem: i dont know how iy got to this point but when I open a script in unity, it opens with notepad! i obviously want monodevelop, so i checked my preferences but monodevelop(built in) was already selected. i tried to browse, but i couldn’t find monodevelop anywhere on my computer. can anyone help me out?

check if it is setup it will be where your unity main folder is

e.g: F:\unity4.5\MonoDevelop folder is beside Editor folder if it exists