Selže-li vše, ještě pořád je tu možnost kontaktovat technickou podporu (z tvého prvního linku):

Submitting a Steam Support ticket

If you have completed all of the steps that are listed above and are still encountering this issue, please submit a ticket to Steam Support.

Ensure that you note which steps you have completed in your ticket. Additionally, make sure that you provide the following:

An uncropped screenshot of the error.
An MSinfo (PC) or System Profiler (Mac) report.
A list of the programs that you have removed per the Programs Which May Interfere with Steam article.

You may be instructed to perform operations that you have already completed in this article. If so, please complete them again as thoroughly as possible.

Proč své odpovědi neřadíš pod to, nač reaguješ (jak jsem psal výše)?