My Qilin desktop V5 Series Problems

My Qilin desktop V5 series of problems-general Linux technology-Linux technology and application information, the following is a detailed reading. 1. Software addition/deletion problems:
Click the item in the left list box. No matter where it is clicked, the error remains unchanged: no package cache is available (the package list needs to be rebuilt, which should be automatically completed by the backend)
More details:
Cannot retrieve repository metadata (repomd. xml) for repository: nsld5-base. Please verify its path and try again
2. system update problems:
An error occurred while connecting to the software source:
Error details: Cannot retrieve repository metadata (repomd. xml) for repository: nsld5-base. Please verify its path and try again
After clicking "refresh", the system prompts "invalid software library configuration"
More details:
Cannot retrieve repository metadata (repomd. xml) for repository: nsld5-base. Please verify its path and try again

It seems that all the error messages are the same. By the way I can access the Internet, Access webpages, chat Q ...... No problem.