We need WAY more information. Step one: as @Community member often says, read back the ACD registers and make sure they are configured as you expect. Show us the register values.
You say "if doesn't work" - HOW doesn't it work? What values are you expecting? What values are you getting? What is your input signal? How long does it take for the ADC to report that the oversampled conversion is done? Is it the amount of time you expect given your configured sample time and number of over samples?
