EVERYTIME i go to flags tab of an object hammer freezes for a second, then closes. The only way i can go to flags is by opening the object box, closing it, opening it again WITHOUT opening other objects in the progress, and THEN go to flags. This is annoying because i keep forgetting it and i lose work. Please help.

There may be an error in the Hammer entity information file for Portal, which, among other things, tells Hammer which properties and flags each entity type supports.
To refresh that information, bring up the Source SDK launch pad and select "Reset Game Configurations". (This doesn't delete your saved games, achievements or settings.)

If that doesn't help, try un-installing and re-installing the Source SDK entirely.