When u tried compiling the second game what exactly happened? qb must have given u an error. Please mention it so some one can help.
As for a good source to download qb4.5 or qb7.1 please search with keywords like qb4.5, download, free, complete version etc.
P.S. I think u must have accidentally deleted some files which were required by qb when u tried compiling the second game.