i was using two powerful range weapons. the game locked up or crashed and when i restarted from the last saved, those two weapons wouldn't do any damage. but my melee weapon would. i finished the battle using the melee weapon. after the battle, i repaired the two range weapons and then they went back to normal. those two were one of a kind weapons. has anybody else had the same problem?

Maybe you should tell us what these weapons are so that we can help\tell if we have had the same problem.

perfortator and destabilizer but after i repaired them, they worked like they should though they weren't that damaged.

also i noticed sometimes nasties which seem to be in a fixed position, aren't there. i noticed a couple of times the super mutant nest near rivet city was missing the nasties.

That's not uncommon. There's lots of spawn points where the first time you go through certain creatures don't appear, but the next time through they will be. Creature spawning isn't necessarily a fixed thing in this game, there's always some variations, which make things a bit more interesting IMO. If you really want those ones to appear, just save your game then reload, they'll probably be there then.