Ums abzukürzen (Quelle: http://www.uesp.net/wiki/Oblivion:Ahdarji%27s_Heirloom
The ring you're looking for may not be in the jewelry box.
This can happen under a number of circumstances:
1.If you talk to the maid and then a guard and don't talk to Ahdarji before opening the box.
2.If you first talk to Hlidara Mothril to find out about the countess taking off the ring at night, and then talk to Count Marius Caro who tells you to talk to Hlidara Mothril.
3.Reportedly, if the countess is sleeping on the left hand side of the bed, this bug is likely to happen. Just wait outside the castle for a couple of days and try again. If the countess is on the right hand side of the bed, the bug will be fixed. One possible reason is that the countess usually sleeps on the right side of the bed (where her jewelry box is), and she would usually place her ring in the box before going to sleep. But if the count sleeps on the right side, she will have no choice but to sleep on the left side of the bed. Consequently, she will also forget to drop off her ring in the box.
On the PC version, use the console command player.additem 00035E95 1
to add the ring to your inventory and complete the quest.Otherwise, head outside the castle and wait for a couple of days or more, then go back in and the ring may appear in the jewelry box. You may need to try waiting multiple times, but it has been confirmed that this fix does eventually work.
Another possible fix is to kill someone who belongs in the quest like the countess' bodyguard. You will get a journal update that you have to pay the blood price. Pay the price and you will automatically complete the quest, even if you had no rings, this also works with two rings. However, this fix may not work for all players. There have been reports that the option to pay the blood price may not show up in conversations with S'Krivva even after killing, for example, the countess' bodyguard.