This problem is going on since there has been a patch. There are a couple of reports on the steam forums but no solution yet.

I also contacted customer support about a week ago and have not received an answer.

I tried reinstalling the program (which causes an error now as steam is no longer directly linked to the installation but works with a workaround) and also disabled my anti virus program (eset) but it does not help. Vegas only crease a "dead" process, but doesnt start up.

You can find posts on steam here:
http://steamcommunity.com/app/523120/discussions/0/2765630416815492855/
http://steamcommunity.com/app/523120/discussions/0/1496741765135603710/
http://steamcommunity.com/app/523120/discussions/0/1520386297684408585/
http://steamcommunity.com/app/523120/discussions/0/1520386297686885358/
http://steamcommunity.com/app/523120/discussions/0/1520386297694370528/