Who can help me????

first of all, disconnect the cd-rom and harddrive phsyically from your notebook.
warning: the connector for the harddrive is a little bit fragile ->
pull on the right and left foots to open it up.
now pull the ribbon cable out.

if you are unsure, you can use this owner guide  from the dell website.

format a usb stick with RUFUS tool.
Select first the USB stick you want to format.
Warning: All data on this USB stick will be lost.
Use MBR partition scheme for BIOS or UEFI, FAT32 (Default), Cluster Size 8192 bytes (Default).
The volume label doesn't matter.
Set a tick at quick format.
Untick "Create a bootable disk using..."
Untick "Create a extended label and icon files"

Download the UEFI version that was at last on your notebook.
if it was version A07, then download A07.
if it was version A10, then download A10.

Extract from 3350A10.exe / 3350A07.exe the UEFI file.
Open up a cmd and enter the following command: 3350A10.exe /writehdrfile
Rename the rom file to 3350.hdr and move it on the usb stick.

Disconnect the battery from your notebook.
Plug In the pendrive.
Press the end key and hold it down.
Connect the charger (still hold END).
The notebook starts automatically and shows the recovery screen.
Press enter and wait until finish the flashing.
Press any key to restart.
The first restart attempt wouldn't be successful.
The second one would work.
Give it a little bit time between the start attempts.

quote: http://macxylo.blogspot.de/2016/08/dell-vostro-3350-a10-bios-mod-v01_5.html