Some ways to fix Steam
Rebuild your ClientRegistry.blob
This is pulled off the Steam KB
Completely exit from the Steam client.
Go to C:\Program Files\Steam (or the Steam directory that was specified during installation).
Locate ClientRegistry.blob and rename this file to ClientRegistryOld.blob.
Restart Steam to allow the file to be recreated.
Test the issue once more.
Watch out for other programs!
It is known that programs such as Airfoil and F-Secure may cause problems with steam. Valve lists many of them here. Try toggling your virus protection, firewall, etc. to see what is causing steam to be unhappy. Try starting your computer in safe mode by pushing f8 before the windows logo comes up.
Try out the Steam Fix Program
This program claims to fix a wide variety of issues. Simply run it and follow the directions. The downloads are on various KB articles such as this one.
Validate game cache
If a game is having problems, rather than mess around with installs, try validating your cache! Cache validation is accomplished by right clicking the game in library and clicking the Local Files tab on top. Now, click the button that says Verify integrity of game cache. Be patient as this takes a long time
If all of this fails...
First, try a restart of your computer. Give steam another shot and if it doesn't work, it's time to reinstall. In this steam KB, it is outlined how to do a complete reinstall. ALL OF YOUR STEAM FILES WILL BE GONE. Please, make sure you know your password and you are willing to wait for games to re-download. If you want, move your steamapps ( C:\Program Files\Steam or C:\Program Files(x86) )
- Make sure steam is closed
- Open Control Panel
- Select Add or Remove Programs
- Scroll down to Steam
- Double click Steam
- Use the automated uninstall process
FOR ADVANCED USERS:
If you really want to wipe out your old install, head over to your Program Files or Program Files(x86) folder. Find the Steam directory and delete it. And, with regedit:
For 32-bit operating systems:
In the left-hand column of your registry editor, navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Valve\.
Right-click on Valve and select Delete.
For 64-bit operating systems:
In the left-hand column of your registry editor, navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Valve\.
Right-click on Valve and select Delete.
In the left-hand column of your registry editor, navigate to: HKEY_CURRENT_USER\Software\Valve\Steam.
Right-click on Valve select Delete.
Don't do this if you don't know what you are doing, and please, make backups.
I have now discovered the issue (after posting, of course). I have a Ralink RT2860 wireless card that I use to connect to the internet, and the newest (albeit three years old) drivers apparently cause the issue.
If anyone else has this issue, you can download the working drivers (version 3.0.11) from this link.
Best Answer
In most cases it's practical to start troubleshooting a malfunctioning program by running it as an administrator of your system.
This is likely not the cause here, but it can help speeding up the process.
Temporarily disable any third-party firewall, anti-virus software (Windows Defender usually plays nice, for a change), or other intrusive software, and try restarting Steam.
Take caution, as this will also temporarily leave your system vulnerable, so be sure to re-enable directly after a problem is fixed (that is: disable only during that window of restarting Steam).
Try deleting that Libswscale-4.dll file: it surely is a newer version of Libswscale-3.dll, and, in any case, if Steam is missing files, it will redownload them.
There are a few more fixes explicitly for your case mentioned in this Steam Community thread, most successful of which seem to be (or seems to be a combination of) the following steps [edited slightly for readability]:
and
Now, before you try this in Safe Mode, I suggest deleting the mentioned files - as administrator - in the normal Windows mode, creating a shortcut, adding those parameters, and running it - as administrator. If that doesn't work, you can always fiddle around in Safe Mode.