I'm having the same problem I've seen many people post on here and elsewhere on the web, sometimes resulting in dead-ends or very obvious answers.
Mine is one of those dead ends - every time I try to enable file and printer sharing in my Windows 7 Professional 64 bit PC, I click apply, it closes, and then I click on the advanced settings to check and see, and sure enough, it's disabled again.
All the correct services are running, I even went as far as resetting the firewall to default, and ensuring nothing was tampered with in
services.msc, as I mentioned before. In other words, I've tried everything I can think of, and everything everyone else seems to be able to think of, but file and printer sharing will stay turned off under any type of network setting or homegroup setting.
I've been able to use file and printer sharing on my other Windows 7 Professional installs that have mostly the same software installed as on that is being "difficult."
I'm stumped. I don't think I've ever been so lost that I had to myself post a question on a forum for a windows related issues, and I've been working in this field 15 years! (that's how baffled I am, :)