What are my rights?

I have a Lenovo notebook and the problem that the CPU no longer clocks up since the last repair, according to the dealer. In addition, Lenovo scratched the back case of the notebook for the last time. Now we have sent the device to Lenovo for repairs and case exchange and it came back after 2 weeks. Lenovo did not repair anything despite the accompanying photos, but scratched the entire backcase even more. These scratches are so deep that they must have been scratched with a sharp object. How can I proceed against Lenovo if they refuse to exchange the case again and refuse to repair it? Unfortunately, I have no warranty rights against Lenovo. Do I have to exercise a guarantee against my dealer? Actually, I would like to avoid that because we have had stress in the past because of another notebook. The device is now 1 year and almost 4 months old.

I can't rate that with the CPU and the clocking up, that's a technical problem and in principle only the base clock is really guaranteed permanently, the boost clocks for a few milliseconds at most. Due to a BIOS / UEFI update, it may be that the heat and consumption settings have been changed in such a way that the CPU is no longer allowed to clock high or this is only allowed for a few milliseconds, so that most programs do not display this with their interval measurement. If necessary, you would have to check this with an oscilloscope or the like, which would then have to be clarified by an expert. Something like this should not be a problem for the dealer after 1.4 years, as it is no longer covered by the warranty (warranty means that a defect already existed at the time of handover, which, according to you, does not apply to you).

The one with the scratched case is neither covered by the warranty nor by the guarantee, since it was not a defect that already existed at the time of purchase or was caused by material defects. This falls under the liability for services. The problem You have to be able to prove the condition both before and after submission. A possible support could therefore be a log from the dealer where you bought the device and returned it for repair. From experience I know that most dealers hardly carry this or hardly note any damage, so I see little chance for you if this damage applies unless you have before / after photos.

In both cases you have to proceed against your dealer, because you have a repair contract with them and are therefore liable. The dealer can then take recourse against the workshop or Lenovo.

If my dealer were to stand by as a witness, it would be different, wouldn't it? He inspected the device before shipping it.

He could just act as a witness that the damage was not there before shipping. But since you would first have to direct your claims against him that might not make him so happy.