Acrobat Reader 4.5 won't open

I have Reader 4.5 downloaded but it will not open.  I had it previously and then it quit working so I uninstalled and then re-installed and it work for awhile then it quit again.  So I uninstalled and re-installed and now it will not open at all.  I also, have Reader 3.0 on the same machine and it will open but not let me open any books.  So what do I need to do so that I can use Reader on my laptop, I also, have it on my desktop and it works but not on my laptop.  Thanks.