Several games aren't working

I bought a Windows 8 desktop PC from Overclockers back in February, its been running fine up until now, however lately I've noticed games not working. Games loaded on Origin as well as certain games on Steam aren't working. I have got an error message that appears when I try to load up the Steam port of Sonic Adventure 2. Can someone help me out here please?

Here is the error message:
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.ArgumentOutOfRangeException: InvalidArgument=Value of '22' is not valid for 'index'.
Parameter name: index
at System.Windows.Forms.ComboBox.ObjectCollection.get_Item(Int32 index)
at Launcher.MainFrame.SaveUserConfig()
at Launcher.MainFrame.SaveConfig()
at Launcher.MainFrame.StartButton_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.5477 (Win7SP1GDR.050727-5400)
CodeBase: file:///C:/Windows/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
Launcher
Assembly Version: 1.0.4645.23848
Win32 Version:
CodeBase: file:///C:/Program%20Files%20(x86)/Steam/steamapps/common/Sonic%20Adventure%202/launcher.exe
----------------------------------------
msvcm90
Assembly Version: 9.0.30729.6161
Win32 Version: 9.00.30729.6161
CodeBase: file:///C:/Windows/WinSxS/x86_microsoft.vc90.crt_1fc8b3b9a1e18e3b_9.0.30729.6161_none_50934f2ebcb7eb57/msvcm90.dll
----------------------------------------
System.Windows.Forms
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.5468 (Win7SP1GDR.050727-5400)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.5467 (Win7SP1GDR.050727-5400)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.5467 (Win7SP1GDR.050727-5400)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
<system.windows.forms jitDebugging="true" />
</configuration>

When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.

Can you please give a small list of the games that both are and are not working?

Did any games stop working? Or you just hadn't tried them?

Have you tried running memtest86, and/or prime95 to see if the system is stable?

Confirmed Battlefield 2 and 3, Sonic Adventure 2, Star Wars Battlefront (goes through to the main menu but I can't do a thing after that) Sonic Generations on online mode, basically any game that connects to a network.

So which games are working properly then?

Emulated games, games with no networking. Sonic Generations works fine until I go to check my online rankings.

Could Windows Firewall or your third party antivirus/firewall software be blocking non-browser internet connections?

@c627627
Wouldn't steam just display an error message saying that you are currently unable to use online features / or that you are currently not connected to steam?
However it might be worth checking the settings anyway.

I almost think this is a firewall issue as well. IIRC, when you start steam you get that annoying firewall/network popup (upon first installation). Then the first time you run a game you also get a popup as well.

Check in CP\Programs\Programs and Features--> "Turn Windows features on or off" to see if both .NET Framework 3.5 (includes .NET 2.0 and 3.0) and 4.5 are enabled.

I do not see .Net Framework 4.5 in the windows features list even though I have it installed. This seems to be related to the problem.

have you tried System Restore?