Others have said things pretty well.
Step 1: Tactics check. Is the player being dumb? If he is, he should stop and see if the problem goes away.
Step 2: Equipment check. Does the character have appropriate gear for his level? A barbarian with a +5 moderate fortification mithral breastplate, belt of giant strength +6, and amulet of health +4, gloves of dex +4, and a ring of protection +4, a +3 adamantine animated heavy shield, +5 vest of resistance, boots of speed, cape of the Montebank, a few potions of fly, and a +1 keen holy cold iron greatsword is going to do a lot better than one with a +1 keen greatsword, gauntlets of ogre power, and a +2 chain shirt.
3. Tactics check two. A barbarian who picks up greater magic weapon, magic vestment, shield of faith, stoneskin, and inspire greatness/inspire heroics from his allies does a lot better than one who doesn't.
4. A little analysis. A barbarian who carries a bow (at 16th level, +1 flaming is pretty cheap) and uses it when the situation calls for it is a lot more effective in any situation where charging in isn't the best plan. If he has Quickdraw or a glove of storing, he can be the one who just takes a 5' step and full attacks the giants when they come charging up. A melee guy who is flexible is far superior to a melee character who isn't. (I play fairly regularly with a sixteenth level fighter/barbarian who I took Quickdraw and Rapid Shot to be able to unload with his bow in the first round and then full attack the bad guys after they charge him--for a lightly armored multiclass mutt, two levels of ranger to make that tactic work even better would be a good investment). Another key situational boost for a melee character is having a ghost touch weapon. Incorporeal creatures are pretty hard for most characters to damage, but a character with a ghost touch weapon does very well.