The CPU fan speed does seem slow. Perhaps opening the case and giving everything a good clean to remove dust and a check of the freedom of the CPU fan is in order. CPU fans are quite cheap and easy to replace so this is worthwhile.
As for the power button, a new case would fix the problem but a visit to your local PC shop/spares/breakers may well provide a far cheaper replacement part. It doesn`t need to be a Medion part simply one that will fit the existing case.