My webshop is offline and gives error undefined class constant CACHEGROUP

I hope someone here is able to help me. I have no experience with technical issues in Magento. I am getting an error while starting my website. Somebody similar to this problem? Hope you can bring me online!

error:

Fatal error: undefined class constant & # 39; CACHE_GROUP & # 39; in /home/deb126395/domains/lapparts.nl/public_html/app/code/core/Mage/Core/Block/Abstract.php on line 1075