When you go to launch S2K, it displays the update screen briefly, then quickly goes away with no errors; open the event viewer on the PC and and check application errors. Look for the most recent one and if it references a .net runtime error, try doing a repair on the .net framework (through programs and features in control panel)

If you see the log reference kernelbase.dll go to the s2knet folder on the C drive, find s2k.exe > right click > properties > compatibility > then select compatibility mode for windows xp service pack 3 and check the box to always run as administrator.

Many times, simply re installing s2k will get it back to normal. It is a cloud based program so none of your data or settings will be lost. Open your C drive, find the S2KNet folder, rename it to something else like S2KNetOLD or S2KNet_ (underscore). Click this link to re download the program:  http://ftp1.s2konline.net/S2K.exe

Another thing to check is if any security software installed on the PC. Try shutting it off temporarily to see if S2K will work when it's off. If that is the case, contact your IT department to set program exceptions for s2k in your antivirus software.