Hello there ,
Here’s the deal :
I was in matrone’s lair , trying to kill uber andariel , but I died against minions just before .
I tried to retrieve my body , but the minions were too strong so i left the game.
Just afterward I made a new game to retrieve my body and my stuff but surprise , i only retrived some of it.
I lost helmet staff ring belt boots gloves amulet .
What should / can i do ?
There is nothing you can do.
You died more than once which led to more than one corpse in the game BUT! only 1(!) corpse is saved when you leave a game. So anything not on that saved corpse is lost.
Alright thanks !
won’t happen again for sure 
I’ve got the same problem, 2 times precisely at the same spot: Claw viper lvl 2. You can’t run away there, and The snakes where to strong. The first time I was lucky to kill the monsters at the end, but with a LOT of effort. This time I am not so lucky with my sorcerer. So I left this game, and start a new one. But when starting the new game my fully equipped body came with me. Was I seriously very lucky or is this problem wich Steak comes with solved now? because I tried about 10-15 times to kill the snakes, and died just as often.
Best guess: your 1st corpse had all the gear and all others were empty (you equipped no backup stuff). The game saves only the corpse with the most gold-value and with all corpses but the 1st being empty your 1st corpse was saved and you got all your stuff back.
Beware however: there is a maximum amount of corpses you can have in a game. AFAIR it’s 16. If you die more then (max corpses) older corpses will be destroyed so you can still lose everything by dying too many times!
FYI: Steak’s problem was that he had multiple corpses and none were empty. Perhaps he picked parts of his 1st corpse but could not store everything so the corpse stayed with some items remaining on it.