However, as others have mentioned, you can run Steam in offline mode as well.
There is no easy way to make the client always boot in offline mode.
Yet steam works perfectly when I login to windows 7 without any issues.
Seems more like a Windows problem than a Steam one.
Navigate to your Steam - Repair Folder Sometimes files on hard-disks and other storage devices become corrupted because of bad hardware, software crashes, power surges etc.
Steam can verify the correctness over installed game files and fix them if necessary.
Sometimes these user permissions break and need to be refreshed.
The steam client for downloading PC games has stopped working correctly where it used to download without issue about two builds ago.