You should update your system ASAP, windows7 no longers supported by Microsoft, but you can try some things:
Add L2 Folder to Exceptions of windows defender or your antivirus, o directly disabled it and then start again.
1. Delete your System folder (and Data folder if you have it).
2. Download again and extract everything again and place Updater in your root folder (example /Lineage2)
3. Open Updater as Administration.
If this not work try to update your windows, for the currently l2 client you should have the "
Security Update for Windows 7 for x64-based Systems (KB3033929)"
After install it restart your computer and run the Client using the updater.
This article lists the download links for the latest versions of Visual C++ Redistributable packages.
support.microsoft.com
https://www.microsoft.com/en-us/download/details.aspx?id=46148