Firstly, please make sure that your OS is up to date, including Service Packs.
Then please go here, click on the red Download button, and:
- if you are using 64bit operating system download both vc_redist.x64.exe and vc_redist.x86.exe, or
- if you are using 32bit operating system download only vc_redist.x86.exe.
After the download is complete, install the downloaded files. If you downloaded both files, run vc_redist.x86.exe first, and vc_redist.x64.exe second. Please make sure to run the installation as an administrator. To do so, right-click on the file and select "Run as administrator" from the drop-down menu.
If for some reason you can't install aforementioned updates or redistributables, and you meet the requirements, please check in programs and features, if you have them already installed. If you do, please try reinstalling them.
After the redistributables are installed , GOG Galaxy should work properly.