One thing you can try to do is to re-spec into a Trap Assassin, primarily using the Lightning sentries to kill monsters.
You could probably do some sort of fun PvM build by making a bear sin (Beast runeword weapon with Pride helm and/or shield), though those pieces of equipment are quite expensive.
In general, melee Assassin builds are better served for PvP rather than PvM. Pretty much all builds will struggle in Hell without some decent gear to put on your character. Unfortunately, Diablo 2 is a very, very item dependent game, which is probably why you are struggling on Hell mode.